As in the original series, Kaiba is sarcastic, offensive, and all around not very nice, and this was just for Episode 1 (In Episode 24 he does admit he's an asshole, just like his past self). He evidently likes to "screw the rules" due to his large fortune (one of his most popular phrases from the series is "Screw the rules, I have money!" Despite the fact that he hasn't said the full line since the first episode) Kaiba uses the phrase 'Sick Bastard'. He is unable or unwilling to help the protagonists, such as calling an ambulance in Episode 1 or fighting Anubis in the Abridged Movie. He explains this by "being obscenely rich", and can't be expected to do it [himself].
The spot in his heart for Mokuba seems to be gone, for whenever his brother talks he replies "Shut up Mokuba". However, this might be due more to his abridged personality more than anything, as Kaiba never seems more annoyed than usual at the more irritating bits of his brother's antics. As in the original series, the card he wears is an oversized locket, with a picture of Mokuba inside. It seems that Kaiba has two motivations in life: money, and his little brother. But money does come first.
Also he admitted that he flags YouTube to compensate for his small penis size, but this remark was most likely a jab from LittleKuriboh to the people who flagged his videos on YouTube, resulting in his ban.
He disappears for several episodes due the fact he was written out of the show, but returns to help Yugi defeat his "ghost" in Episode 7 (although unlike the original, he isn’t much help at all). He may also be addicted to drugs that affect his memory; in Episode 11 he thinks he used to have green hair when he first dueled Yugi (using clips from the first Japanese series. His catchphrase appears here as "Screw the rules, I have green hair!"), and in episode 44 when a robot from the future (The Cybernetic Ghost of Christmas Past From the Future) tells him to use his Blue Eyes instead of Obelisk, which again he believes to be caused by drug use ("Man, I really need to cut down on the drugs.). He also comments that he has "Leet haxor skills" (Or 1337 h4x0r 5k1775), apparently having learned all his hacking skills from watching old episodes of Star Trek (as his computer comments on his typing the same keys repeatedly). He also stated that the "Blue Screen of Death" was his mortal enemy in the same episode.
It is hinted that Yami's Mind Crush in episode 1 may have given Kaiba brain damage, as he states in episode 35 that he can't remember the events of episode 1, also claiming that he might have given him brain damage. This is revisited in episode 56, where he seems to be unable to hear or say the word "Exodia" without saying, "Ah! Exodia! It's not possible! No one's ever been able to summon him!" While the first two are in astonishment at Gozaboru summoning Exodia Necross, after Kaiba declares that he will destroy the pieces of Exodia in Gozaburo's Graveyard he suddenly exclaim, "Ah! Exodia! It's impossible! No one's ever been able to destroy him!" causing Gozaboru to ask him if he's alright; suggesting that Kaiba suffers from either brain damage or Post-Traumatic Stress Disorder.
Abridged Kaiba also has an even more distinct obsession with dragons than his counterpart. He claims that, while he plays chess, the game bores him because it doesn't include expensive holograms or dragons. However, In Episode 48, it is revealed that he was the chess prince, a fact that he is extremely proud of. He was once even told by Yami that he has a dragon fetish. He also mentions having a hard on for technology. He also ranks Reign of Fire as one of his all-time disappointments in life. He is apparently easily impressed by giant rocks. He also holds the ability to frequently break the fourth wall without any explanation and does so more than most characters. He also disregards anything involving Yu-Gi-Oh! GX and is appalled by the idea that he only appears in 3 episodes of said series (mentioned by Bakura to be one episode). He also is highly skeptical of Ishizu Ishtar's prediction that in 10 years during Yu-Gi-Oh! GX he will have opened a Duel Academy and not have aged a day.
Also like in the series Kaiba seems to be against the magical powers some of the cast has. In episode 6 he thought his duel disks could defeat Yugi's magical powers and in 24 he mentions he's the most skeptical person on Earth. He does seem more accepting of the magic than the actual Kaiba, even though he still believes Ishizu's powers to see the future are lame and full of crap.
Recently, Kaiba has attempted to play Duel Monsters with a training program (which was a parody of GLaDOS from Portal), claiming that actually learning how to play the game would help him defeat Yugi since, as a main character, he is immune to defeat. However, the training program claimed the game was so ridiculously complicated that it has decided to take Kaiba's policy and screw the rules. Throughout episode 26, he has been advertising Kaiba Corp. products, specifically the new DUEL DISK SYSTEM, which is accompanied by a jingle, and an echo. Through this episode, after he advertises products, he says the word, "Trademark." He has also announced the coming of the Battle City tournament, which will follow the real Duel Monsters rules, something which Yami believes is the first real plot twist in the series. Episode 26 ends with him losing a finger. He is terrified of Dark Zebra, and had Obelisk the Tormentor kill it for him but mentioned how Dark Zebra would haunt his nightmares forever. He is quick to have his finger replaced by a replica, he is also horrified to find out that Mokuba is going through Japanese puberty and thinks he is a Pokemon and even Kaiba got confused about it when he once called him Charmander. He has also created a harem of robot women so he can get them to fall in love with him only for him to later shun them with his cold heart. He has acknowledged that he is like the anime version of Scrooge McDuck, except less fluffy (surprisingly, in agreement with Mokuba). He also reveals that he prefers window seats on all vehicles.
In the other Abridged Movie, he is shown spying Yugi with cameras installed all over Japan (since he is rich, he can never be too paranoid) in order to always be one step ahead, even in private moments like the shower (Yami is confused when Kaiba mentions that he won't be watching him take a shower). He starts a tournament to defeat Yugi again and to do so, he orders Kemo and an anime version of Ving Rhames to kidnap Gary and force him to enter. Before facing Yugi in the tournament, he defeats Rex Raptor who then goes to dye his hair. During the duel against Yugi, he summons three Blue Eyes White Dragon in one turn again. When Yugi asks him in the same fashion as in the episode one about what he did, Kaiba tells him to stop asking about it. After losing, he decides to sue the people who made Eye of Judgment for the PlayStation 3 (stating that it's an obvious rip off of Duel Monsters) and asking where Mokuba is.
Lately, he was been informed by Mokuba in "Seto Kaiba's Real Father" that his 'real father' had contacted them via a blackmail letter (with the writer demanding his share of KaibaCorp's money), but in the concluding video "Kaiba's Real Father - Conclusion" he attempted to uncover his father's identity and to make him pay. This led him to Pegasus (because "every time something f*cked up happens, you show up and start explaining things!"). Pegasus agrees to tell Kaiba who he would need to see to find out who his real father given that he did something dirty in return (which was watch the Spice Girls movie). Kaiba later ends up meeting the Cybernetic Ghost of Christmas Past From the Future (whom Kaiba met in a delusion during episode 44) who informs him that Kaiba has no father and he is actually a 5000 year old cybernetic organism built by the Egyptian Slaves under the command of invading alien force leader Frieza from Dragon Ball Z abridged. He was made to resemble the Egyptians previous leader Priest Seto who became Pharaoh after Atem died. This makes Mokuba query that if Seto was a robot and didn't have a father, who was his father, in which the Cybernetic Ghost of Christmas Past answers "Ghost Nappa", which Seto and Mokuba had earlier stated that knowing their luck it would turn out to be something like that.
Kaiba is also extremely misogynistic, having little to no regard for the female sex. He created a harem of female robots, (revealed in episode 30) but reveals it was only so he could "shun them with his cold indifference". Grandpa, Tristan, Bakura, and even Kaiba's own computer have mentioned that he needs to get laid...big time. Also, when asked by Mokuba where babies come from, he impatiently answers "you buy them in a store, just like everything else." Though he was curious about his "totally hot dragon girlfriend from the future" that the Ghost told him about in episode 44 and even asked if they had sex ("Yes!") and whether it was good ("No!").
Kaiba has had a boner twice (seemingly from technology, as he stated in episode 15), once before riding on a helicopter to go find a God Card and once while watching Bakura and Yami duel on the blimp. At the start of the duel, he says that he'll stand there and pretend he doesn't have a boner and later in the episode, doesn't care what the duelists do, as long as no one looks at his crotch.
It has been stated that whenever Kaiba smiles a puppy dies. In Episode 42 he smiles twice and manages to kill 9101(19101 if you count the parody of the abridged series) puppies; killing 100 when Odion summons Mega Ultra Chicken and 9001(its over 9000)when Melvin informs the main characters that he got Team4star banned. He also practically begs Mai to summon Mega Ultra Chicken in episode 43. Kaiba has said that he never takes off his clothes stating that they made him look good. He also has a really embarrassing birthmark that's covered by his clothes.
As revealed in Seto Kaiba's Real Father Part 2, he is a robot designed for building pyramids, created in Egypt (Apparently, this explains why he is emotionless and lacks genitalia and his birthmark that says "Made in Egypt"). Due to the fact that the Cybernetic Ghost of Christmas Past From the Future's stories seem to be random and made-up, this may or may not be true.
In Season 0 abridged, Kaiba's personality is much different. He is open and friendly, yet still has some of his selfishness, as he orders his bodyguards to beat up Joey, Tristan, and Yugi, declaring that while he likes them a lot, he just likes money more. He also plays a Shadow Game (feeling it enhances the game playing experience) with Yami just for fun, and at one point offers him a hug. Also, after he summons a bunch of monsters in one turn, he actually tries to explain how that is, in fact, within the rules! Kaiba's new personality frightens Yami so much that the Pharoah uses his dark powers to banish Kaiba to "a place where he cannot hug him."