Ferus Olin was the human Jedi Padawan of Jedi Master Siri Tachi. Due to his masters friendship with Jedi Master Obi-Wan Kenobi, Olin worked alongside Kenobi and his apprentice, Padawan learner Anakin Skywalker. The two Padawans often clashed despite working together on numerous missions. Skywalker was considered the most-gifted apprentice with Onlin being the second. This created a hostile enviroment between the two Padawans, with Skywalker being the only Padawan to dislike him. Olin, shortly before the start of the Clone Wars, ended up resigning from the Order due to guilt over the death of fellow Padawan Darra Thel-Tanis on the planet Korriban.
Later, Olin befriended the human Roan Lands on the planet Bellassa and they started a business together, producing fake identities for those fleeing the empire. He also founded a rebel organization on Bellassa to fight the newly-formed Galactic Empire. Olin would later retrain himself in the ways of the Jedi with the instruction of Obi-Wan Kenobi, one of the few Jedi survivors of the Great Jedi Purge. Olin also constructed a safehouse on an asteroid well-hidden by an atmosphere storm to hide fugitive Jedi from the Empire, forming the early stages of the Alliance the Restore the Republic.
While Olin searched for fellow Jedi survivors, he was forced to aid Sith Lord Emperor Palpatine or else his friends Roan Lands and Dona Telamark would be executed. Olin, however, would act as a double-agent. He eventually confronted Darth Vader himself, not knowing it was his former rival Anakin Skywalker. Olin, upon learning Vader had killed Roan Lands, gave into his rage and anger.
Olin's resistance movement was wide-spanned until his secret asteroid base was destroyed by the Empire. He then fulfilled a request by Obi-Wan Kenobi to watch over Princess Leia Organa on the planet Alderaan. When he realized out Organa is Force-sensitive, he demanded answers from Kenobi. When the Emperor arrived on Alderaan, Olin realized Vader's true identity as Anakin Skywalker. Vader was unperturbed by Olin's newfound knowledge of his identity and the death of his wife, Padme Amidala, and the two began to duel, leaving Olin alive but grievously injured. He continued to watch over Princess Leia Organa. He was active in the Rebel Alliance until eventually meeting his end when he sacrificed himself to allow Organa and numerous prisoners to escape. He battled Darth Vader, but was eventually slain by the Sith Lord.
Ferus Olin was intended by author Jude Watson to be a gay character with his spouse being Roan Lands-creating a parallel between Olin and Vader. Both characters give in to the dark side after the deaths of their spouses (Roan Lands and Padme Amidala respectively).