Little is known of Smith's background. We know he had a Great Aunt Maude and cousin Jeremiah Bouleregard Smith (CURSE OF COUSIN SMITH), a Great Uncle Thaddeus, possibly a first Uncle Thaddeus, an Aunt Matilda (all three from GHOST IN SPACE).

One of the Thaddeus's found the Comstock Load all by himself (we don't know which Uncle this was - Great Uncle or just Uncle). Smith's great-great grandfather was a 49er miner. There might only have been one Uncle Thaddeus.

As a youth, Smith spent many summers on his Uncle Thaddeus's farm where he won first prize at the County Fair but not for the tomatoes (and the Robot seems to know this in THE GOLDEN MAN).  Aunt Maude died under mysterious circumstances, Smith was at her bedside; Jeremiah gave her medicine shortly before she died but a coroner's inquest found him not guilty of foul play.

Maude left a will which gave the last remaining Smith her fortune. The last time the cousins (there were ten of them at that time) tried to settle this peacefully, Jeremiah tells John (and he could be lying) it looked like a bloodbath that made the St. Valentine's Day Massacre seem like a picnic.

On his mother's side the name is Ruthven -- at least partly Scottish.  One of the Smiths was a Ruthven who, in 1497, bore witness against Hammish Lu Glamis, 9th Laird of Glamis.  Hammish was subsequently executed for high treason against his liege lord and master James Steward, king of Scotland (from THE ASTRAL TRAVELER).

In THE GALAXY GIFT, Smith claims to Penny that he has an aunt who lives on Knob Hill, not far from San Francisco's China Town.  This might be an aunt on his mother's side, a surviving Smith not known to anyone else, or perhaps a figurative aunt (close friend to the family?) or someone else entirely - a great aunt maybe.

Smith also has a gambling addiction. A look-alike for Dr. Smith, the space outlaw and desperado Zeno of Casseopia, once made an illegal visit to the planet Earth. Smith wears a large ring on his left hand. He also seemed to have his grandfather's timepiece on him or with him since THE RELUCTANT STOWAWAY all the way to THE SPACE PRIMEVALS where a caveman alien guard snatched it from him.

Dr. Smith always loved food and lazing about. Smith also recalls walking hand in hand through nature's wonderland on nice days on Earth but he also claims to abhor nature (THE GREAT VEGETABLE REBELLION) -- it always makes him sneeze (and he does so in DEADLIEST OF THE SPECIES and THE DREAM MONSTER cliffhanger into THE GOLDEN MAN where Penny has flowers near his nose).

Smith claims to have been a medical doctor, a psychologist, a psychiatrist, an expert gourmet as well as a doctor of environmental space psychology. He claims to have known a famous British female cook.

Smith gave teachers apples when he was in grade school, snitched on fellow school mates (such as Johnny Sorenson), played the ukulele (which he used to hide stolen test papers in when in high school and college), sold stolen test answers for 100 dollars, once wore a sportsman shirt with a C on it, and a baseball cap. 

Smith may have taught NY Dodger baseball player Sandy Kofax the dipsy doodle throw (which he professed he did to Will and Penny by the time of the cliffhanger before ROCKET TO EARTH).  Smith seemed to disdain the mention of baseball in WILD ADVENTURE ("Oh yes,THAT!").  He also professes to have been taught a thing or two about pitching from Satchel Page, a Cleveland Indians baseball player who had struggle up in the league because he was black (this was just after Jackie Robinson).  Smith also mentions Joe DiMaggio, Ted Williams, and Babe Ruth. All this despite Smith claiming to dislike sports in DEADLY GAMES OF GAMMA SIX -- "they seem so healthy."

Smith hit and may have killed a guard on the Jupiter II in THE RELUCTANT STOWAWAY (in the original script it was a stun needle on his ring  - or some kind of poison), was fairly selfish and evil minded in most of THE RELUCTANT STOWAWAY, THE DERELICT (where he kills or injures a few of the bubble aliens - which he feels sorry for (somewhat) in PRISONERS OF SPACE),  and ISLAND IN THE SKY (where is at his meanest - forcing Don and Maureen to abandon John on the planet, using the Robot to threaten to crush their skulls, and sabotaging not only John's rockets but the Jupiter's as well!). He did lament having to do away with Will, a somewhat fit companion in all this nightmare. 

After the crash landing, he plots with the Robot, who he has given orders to check on his safety every hour on the hour, to kill all the others with the exception of Major West. When they learn what they needed to know from West, he, too was to have been eliminated.

Smith regretted only having to kill Will.  Smith was a bit more open minded in THERE WERE GIANTS IN THE EARTH and THE HUNGRY SEA even though still hoping the Robinsons would be killed as they ventured across the planet by lightning, earthquakes, monsters, deep freezes, and excessive heat.  Yet, he warns them, not once but twice, feeling perhaps that he needed human companionship - the Robot was still pretty mechanical and dullard-like.

Smith was selfish in WELCOME STRANGER, continued to spy on Penny in MY FRIEND MR. NOBODY, offered Will up to the INVADERS FROM THE 5TH DIMENSION in what must be one of his most evil acts, and continued to plot against the entire group in THE OASIS.

In OASIS it is apparent that John, Maureen, and the three kids have begun to feel something like respect and even love for Dr. Smith and it could also be that the fruit Smith ate, affected his mind for a bit.  He certainly plots the end of the others when he thought he was going to die.

He was not too nice to Will in THE SKY PIRATE and THE QUESTING BEAST, offering Will up as a hostage in both and not caring if the Robot killed Tucker or accidentally hurt Will in THE SKY PIRATE. 

He did seem to care that Penny would be hurt in MY FRIEND MISTER NOBODY.  He spied on Judy and Penny in THE MAGIC MIRROR since his greed made him want the full length alien mirror the two girls were propping up for use. Smith once called Penny, "Penelope" when he thought she was using this mirror to trick him.

He once told Penny her garden would whither and die if the Robinsons left him on Priplanus (ATTACK OF THE MONSTER PLANTS) and in the same episode used Judy's vanishing as blackmail on the family so that Don would take him back to Earth.

He also spied on Judy and Don as well as John and Maureen in THE KEEPER.  Getting back to Earth, riches, power, food, and self were Smith's chief obsessions.  He plotted many a time to steal some alien or visitor's spaceship (THE KEEPER, THE SKY PIRATE, THE QUESTING BEAST, ROCKET TO EARTH, and many, many more).

Smith may have not admitted it often ("your family my boy, not mine" in WILD ADVENTURE's cliffhanger into THE GHOST PLANET) but he may have considered himself one of the family by the time of THE GIRL FROM THE GREEN DIMENSION. Smith was always cautious of the aliens and often misjudged the good ones - such as in THE SKY IS FALLING and WISH UPON A STAR and was good at getting the others or some of the others to his way of thinking (THE SKY IF FALLING where he has Judy and Penny thinking he is right and has Don so on edge that Don nearly curses at him and tells him to shove off of it).

Smith also misjudged the bad aliens - as in THE SPACE TRADER. On occasion, his frantic warnings proved to be correct (THE RAFT, WRECK OF THE ROBOT, and others) but more often than not, he sounded the alarm for no good reason (as in ONE OF OUR DOGS IS MISSING).

Smith used the Robot in the early episodes as his companion and protector but by WAR OF THE ROBOTS, he was treating the Robot quite badly, even admitting this at the end and making up for it by giving the Robot a rubdown with oil for two weeks.

BY GHOST IN SPACE, Smith's mind may have completely been changed into a less evil but still silly and selfish man. The takeoff in THE RELUCTANT STOWAWAY may have affected his personality and mind since he was not protected as the Robinsons were from the acceleration (but that doesn't explain future takeoffs). 

Smith was also traumatized in THE MAGIC MIRROR which he refused to believe wasn't his own nightmare world. Smith left Will in the bog in GHOST IN SPACE, left Will green in THE GIRL FROM THE GREEN DIMENSION, left Penny alone with Ohan in ALL THAT GLITTERS, and did various other inane things, screaming at any remote danger or appearance of anything remotely alien.

Smith sometimes was kicked out of camp (WISH UPON A STAR, ATTACK OF THE MONSTER PLANTS, THE DREAM MONSTER, and THE MECHANICAL MEN).  Due to being ostracized with the silent treatment, he also removed himself in MUTINY IN SPACE.  He removed himself before this at another time in THE DREAM MONSTER where no one protested his leaving.

There was some question as to whether or not he would leave the planet with them in ATTACK OF THE MONSTER PLANTS but most of this seems to be a ploy to get Smith to behave or a joke from Don - which Judy thinks is cruel.

Smith is also left to wonder in CAVE OF THE WIZARDS if the Robinsons would have returned for him if they had been aloft when they spotted him fleeing the alien cave and its influence over him.  John seemed to think he would have to remain out in the wilderness thinking about this (another exile?).

Don wanted to leave him on the Xenian space probe and voiced at least three times in KIDNAPPED IN SPACE.  Smith realized they were always threatening to leave him somewhere in THE TIME MERCHANT ("They were always threatening to leave me somewhere.")  In the same episode, Smith's inherent goodness came through and he couldn't allow Judy, Penny, and his dear William to perish, rushing back onto the Jupiter II to save their futures, even though it meant his being lost in space again.

Smith threw in with Sesmar in THE DREAM MONSTER, but worked with Don to escape and get the Robinson's emotions back.

Smith lost his mind when the Jupiter landed on Earth in the year 1947 through a time warp in VISIT TO A HOSTILE PLANET, capturing Will and Robot, trying to force the others to stay on Earth in this time to be the masters of it.

Smith may or may not have had medical experience (he seems to know what he is doing in THE RELUCTANT STOWAWAY, but Don seems to chide him for not having it in KIDNAPPED IN SPACE but perhaps Don meant mechanical medical history and experience as the patient was robotic).

Smith accidentally causes the ship to crash in ISLAND IN THE SKY, FORBIDDEN WORLD, and HUNTER'S MOON (as Robot says, "A familiar behavior pattern is noted."). He also caused it to go off course some time before TIME MERCHANT and in WILD ADVENTURE made it lose the auxiliary fuel supply, changed its course toward Earth several times, caused it shake uncontrollably and almost caused a fire! In the same episode, he set it toward the Earth's sun!

He also, in the cliffhanger, places the ship in a deadly radiation belt which endangers it for its ride, also thanks to him to the dangerous GHOST PLANET! Smith was sort of taken over again in SPACE DESTRUCTORS when he wants to rule the world using an alien machine that makes cyborgs.  It seemed to bring out his more evil side. John almost exiled Smith for good after Will was almost turned into a cyborg for all time. Smith's true apology to John made John give him another chance.

Smith's humanity came out in THE QUESTING BEAST when he regretted every lie he ever told when Will wouldn't believe the truth he told now.  Smith also wanted to save Will's youth and innocence in that episode, one of the first times he acted totally unselfishly and he admitted to Will that rushing to grow up isn't all that worth it.

The other time Smith was somewhat evil was when he was being used by the SPACE CREATURE.  Smith was turned into a hippie (THE PROMISED PLANET), a celery stalk (THE GREAT VEGETABLE REBELLION), and a super strong Samson type (COLLISION OF PLANETS).

Smith also tried to take over the A DAY AT THE ZOO and keep Judy, Don, Will, and Penny as well as the Robot (whom Penny talked into helping them) as specimens in the cages. Don used his laser to threaten Smith in ZOO and THE FLAMING PLANET, something Smith once almost did to Don in THE RELUCTANT STOWAWAY.

Smith abhorred guns as early back as WELCOME STRANGER but took one any way. By the time the show ended he wouldn't really carry one or even hold one.

Smith tricked Judy into becoming a SPACE BEAUTY in Farnum's fashion contest unaware it would have dire consequences for her and sold the Robot to THE SPACE TRADER and the Junkman of JUNKYARD OF SPACE for food both times.

He lied to Maureen in RETURN FROM OUTER SPACE about the omelet, wanted to see the future in THE GIRL FROM THE GREEN DIMENSION, conned Will and Penny and Don and almost every member of the Jupiter II at one time or another, and made countless errors which endangered everyone - not on purpose most of the time (MUTINY IN SPACE, TRIP THROUGH THE ROBOT, THE MECHANICAL MEN).

Smith's double Daddy Zach (who was made out of all the inherent goodness of Smith) sang I'VE BEEN WORKING ON THE RAILROAD a song Smith sang in THE PHANTOM FAMILY. 

Although the most cowardly member of the group, Smith's bravery can be seen in THE SPACE PRIMEVALS (where he saves Don and bonds with the Major, calling him Don for once), THE FLAMING PLANET (where he does save the Robot's sensory tapes), THE TIME MERCHANT, and THE RAFT (where he does pull Will away from the dangerous plants).   

At first, wildly evil (THE RELUCTANT STOWAWAY, THE DERELICT, ISLAND IN THE SKY, THERE WERE GIANTS IN THE EARTH, THE HUNGRY SEA) he began to mellow by THE HUNGRY SEA, and although slipping back to being malicious self centered (ATTACK OF THE MONSTER PLANTS) and greedy (MY FRIEND MR. NOBODY) as well as truly evil minded (INVADERS FROM THE 5TH DIMENSION), Smith really didn't think until it was too late (he cared about the fate that befell poor Judy in VISIT TO HADES, worried about what he did to Will in GHOST IN SPACE, SPACE DESTRUCTORS, and worried about the Robinsons being hypnotized into leaving Penny and Will with monster aliens on THE PROMISED PLANET), and generally was sorry for the harm he would cause.

Smith lied about changing his ways in ISLAND IN THE SKY (Saint Zachary).  After what he thought was A VISIT TO HADES he promised to become St. Pious the third.  He also made similar promises in ALL THAT GLITTERS ("I'm going to finally be the man that you all want me to be!") and THE GALAXY GIFT (but by this time Maureen didn't count on it). He also wouldn't promise John he would try to change in SPACE DESTRUCTORS (the worst reversal of his behavior pattern to date - where he wants to rule the universe with cyborgs).  Both men knew he couldn't change.

Smith also prayed that he would be a hard worker and a noble man in honor of Will, whom he thought was dead in GHOST IN SPACE.   By TWO WEEKS IN SPACE and CASTLES IN SPACE, Smith did seem to be changed somewhat, more an ally than a reluctant castaway, even though he would still dupe anyone anytime to get back to Earth or to get riches.

He did try to save Will from Chavo in CASTLES IN SPACE, was unaware of just how dangerous Judy winning the beauty contest would be in SPACE BEAUTY, went with Robot to find Will and the real Professor in ANTI-MATTER MAN, helped Will overcome the duplicates in TARGET: EARTH (although here he told Earth once he left the Jupiter II they could blow it up!  Will and Robot were still on board!), and cared for Don in FUGITIVES IN SPACE, not wanting to abandon the hurt Major.

By JUNKYARD OF SPACE, he was not the same man, not entirely different (he did sell the Robot to the Junkman).  He told Don in THE SPACE PRIMEVALS, he was trying to find a way out of the cave FOR BOTH OF THEM by enticing a caveman with is grandfather's time piece. This appeared to be true.