Sebastian Krane, formerly known as S-3, is one of the antagonists of Disney XD's Lab Rats. He was the leader of Victor Krane's bionic soldiers and S-1's brother. He first encountered Chase during his attempt to stop Victor Krane's final plan to control the whole world with his Triton App. After Krane was defeated, Sebastian lost his memory and became a student at the Davenport Bionic Academy where he would train to become a hero. However, Sebastian turned evil after Chase told him about Krane, and swore revenge on Donald Davenport for his "father's" supposed death.
Sebastian was a friend of the Davenport family and bionic student at first, but turned bitter when discovering that they destroyed his father, Victor Krane. However, Sebastian did not know that Krane was an evil man, therefore he betrayed the Lab Rats to get revenge.
After Victor Krane was imprisoned, he used the Triton App to activate his bionic soldiers, S-3 being one of them. S-3 led a group of soldiers to break into the Pentagon and steal satellite equipment, before breaking out Victor Krane and S-1. At Pike's Crest, S-3 and the soldiers assembled the satellite equipment, but caught the Lab Rats spying on them before they ran. S-3 then readied his brothers and sisters for battle.
When the Davenports arrived at Pike's Crest, S-3 decided to fight Chase personally, using his laser pitchfork. After a long battle, S-3 lost to Chase. When the Lab Rats defeated Krane, S-3 and the other soldiers deactivated, and dropped on the ground like flies.
After the battle, Adam went back to pick up the soldiers, with S-3 being among them. When they arrived at Davenport's house, S-3 properly introduced himself to Chase, but Chase was uncomfortable around him. S-3 then sent signals to the rest of his brothers and sisters, complicating the Lab Rats' attempts to hide them from the government. Although the government caught up to them and attempted to lock them up, he and a few other soldiers proved themselves good by saving Leo. Donald decided to take S-3 and his brothers and sisters in as students at the Davenport Bionic Academy, with Adam, Bree and Chase as his mentors.
At the Bionic Academy, S-3 decided to have his name changed to Sebastian, as all soldiers needed to trade in their S-numbers for names. Sebastian developed a rivalry with Chase, because Chase was being too controlling and Sebastian kept hitting on Bree. Later on, they decided to work together on a simulator project because Adam kept messing things up. Sebastian wanted to know what happened during the battle, which led to Chase telling him about Victor Krane and how they defeated him. Sebastian did not take this well however, as he sabotaged the project, which led to Davenport needing to go to the infirmary. When everyone left, he secretly swore revenge against Davenport for killing his father.
Sometime later, he discovered that Victor Krane believed bionic humans were superior, and sought to create a world ruled bionic humans were in power. To this end, he recruited siblings Lexi and Tank, both of whom were presumably once loyal to Krane and felt humans aren't worth protecting. Perry figured out Sebastian turned evil, but no one believed her. He later stole Perry's security keys, stole explosives from the weapons vault, and tricked Chase into giving him a new ability. Sebastian then used the explosives to damage the Hydraloop and stranded Perry and Donald in it with limited oxygen. When that happened, Sebastian revealed his true colors to the Lab Rats, that he intends to avenge Krane's death and take over the world. The Lab Rats tell Sebastian that Krane was a brutal, cruel psychopath who never cared for anyone, but it fell on deaf ears. Having seized control of the Academy, Sebastian started a rebellion and turned a group of bionic soldiers against Davenport spreading lies about him. With Leo trapped in the same room as them, Sebastian ordered them to attack Leo while he and his inner circle fought the mentors. When it seemed like Sebastian was about to finish off Chase, Leo escaped and gave the drop on Sebastian. With Leo joining the fight, Lexi and Tank lost, but Sebastian came to. Sebastian revealed he tricked Chase into giving him Davenport's password so he could unlock all his hidden abilities at once. However, using all his abilities at once caused him to fry his chip, and his rebellion was crushed.