Walter Koenig, the boyish actor who remains an integral part of Star Trek lore thanks to his portrayal of the Russian crewman Pavel Chekov, has died. He was 90.

Koenig, also known for playing the scoundrel Alfred Bester on another sci-fi space series, Warner Bros. Television’s Babylon 5 , died Sunday of natural causes in his home in North Hollywood, his rep announced.

Raised in Manhattan as a son of Lithuanian immigrants, Koenig joined Gene Roddenberry’s Star Trek for the start of its second season and appeared on 36 of the 50 episodes that aired in 1967-68 and 1968-69. He also portrayed Pavel Andreievich Chekov in the first seven Paramount movies, released from 1979 through 1991, that emanated from the NBC show.

In a 2013 interview for the TV Academy Foundation, Koenig said he didn’t watch Star Trek before he came aboard.…