Alexsandr Kallus

Alexsandr Kallus is the secondary antagonist-turned anti-hero of Star Wars Rebels. He is skilled in physical combat and rather than leading an attack from afar, he involves himself in the field. After being stuck on one of Geonosis's moons with Garazeb Orrelios, Kallus grew disillusioned with the Empire and began to operate as a Rebel informant until he defected to the Rebellion.

Background
Alexsandr Kallus (former codename ISB-021 and rebel codename Fulcrum) was an Human male Agent of the Imperial Security Bureau before becoming a rebel spy for the Alliance to Restore the Republic. As an Imperial operative, Kallus was a firm believer in bringing order to the galaxy. He worked to suppress dissent on numerous worlds, fighting against the insurgency of Saw Gerrera on Onderon, participating in the genocide on Lasan, and leading the hunt for the rebels of the Ghost on Lothal. He would work with both Grand Moff Wilhuff Tarkin and the Sith Lord Darth Vader.

After surviving with Garazeb Orrelios on Geonosis's moon, Kallus grew disillusioned with the Empire and began to operate as Fulcrum, an informant passing information to the Rebellion from within. He fed the rebellion information about the Empire's activities, including those of Grand Admiral Thrawn, who was tasked with eliminating the rebels.

Thrawn discovered Kallus' true allegiance after realizing there was a rebel spy in his midst, and Kallus was captured as he attempted to feed the rebels information for their planned attack on Lothal. Ultimately, Thrawn discovered the rebel base that was on Atollon and launched an attack that devastated the Rebellion. Kallus broke free of Imperial custody during the battle and was taken in by the Ghost, and accompanied the surviving rebels to the base on Yavin 4, thus escaping from certain execution.

Becoming a full-fledged member of the Rebellion, Kallus assisted the Alliance both tactically and in the battlefield. As a key ally of the Ghost crew, he aided them in their successful liberation of Lothal. After the Empire's demise, Zeb brought Kallus to Lira San, the ancient home of the Lasat people, to show the former ISB Agent that he had not destroyed the Lasat species after all. As a friend to Zeb who turned against his former Empire, the Lasat welcomed Kallus as one of their own. He would then live peacefully with Zeb on Lira San.

Trivia

 * The reason Kallus was not given a first name was because people do not get personal with villains' names. It was only when he became a better person that callous finally deserved a first name.
 * He was named Alexsandr after Star Wars Rebels crew member Alex Spotswood, who always performed as Kallus in the "temp recordings" of the script by the crew during the production of the show since the first season