At the start of Voltron: Legendary Defender, Keith was a dropout from the Galaxy Garrison, despite being considered the most talented pilot of his generation.
[6] After finding Shiro on Earth, along with Lance, Hunk, and Pidge, he joins Voltron as the Paladin of the Red Lion to fight against the Galra Empire.
Later in the series, Keith joins the Blade of Mamora to better understand his Galran half and so Shiro can return as the Black Paladin and leader of Voltron.
Afterwards, Keith continued to practice many other forms of martial arts until he turned 18 and enrolled in the United States Marine Corps, spending several years as a reconnaissance specialist.
Two years later, he was approached by Colonel Hawkins to join a team of outcasts to search for the legendary robot Voltron on the distant planet Arus.