1. Leonard Nimoy

 

After a few uncredited film appearances in the 1950s, Nimoy took his first televised role in the 1953 episode of Four Star Playhouse titled "Knockout" (pictured). Although he played the henchman to one of the main characters, this role was also uncredited. Nimoy would take on dozens more guest starring roles before landing the role of Spock in Star Trek.

Image: Four Star Television

2. William Shatner

 

In the early 1950s, Shatner appeared on numerous Canadian television series, including his formative first role on the sci-fi series Space Command. After a few years in the land of maple leaves, Shatner came to Hollywood in the late '50s to appear on shows like Studio One (pictured), Suspicion and Playhouse 90. 

Image: CBS Television Distribution

3. DeForest Kelley

 

Out of the whole cast, Kelley had the most extensive background on television. His first appearance on the small screen was on the series Public Prosecutor in 1948. One year later, he appeared on The Lone Ranger (pictured). Before he landed his most notable role on Star Trek, Kelley made over 100 (!!!) TV and film appearances.

Image: ABC

4. Nichelle Nichols

 

Nichols didn't get her start on television until the mid-'60s. Her first role was on the series The Lieutenant (pictured) in the 1964 episode "To Set It Right." However, the progressive story about race was deemed to controversial for TV at the time, and the episode was canned. The short-lived series was created by forward-thinking Gene Roddenberry, who went on to create Star Trek not long after it was canceled. In the summer of '66, Nichols popped up as a nurse on Peyton Place.

Image: MGM Television

5. James Doohan

 

Doohan's first role on television was in an episode of Actor's Studio in 1950 called "Sanctuary in Paris." After that, he made steady appearances on shows like Encounter, Playbill and Tales of Tomorrow (pictured). In the 1960s, he appeared on more well-known shows like Bewitched, The Virginian and The Man from U.N.C.L.E.

Image: ABC

6. George Takei

 

Takei's first television role was on the series Playhouse 90 in 1959, followed by an episode of Perry Mason (pictured) later that year. In addition, Takei appeared on a 1964 episode of The Twilight Zone called "The Encounter," which was withheld from syndication for decades after its initial airing due to its content.

7. Walter Koenig

 

Koenig got the acting bug in 1962, when he first appeared on the series Combat! (pictured). A string of guest appearances followed, including The Untouchables, General Hospital and another Roddenberry series, The Lieutenant. 

Image: Selmur Productions

8. Majel Barrett

 

Barrett, who married Roddenberry in 1969, is best known as Nurse Christine Chapel, but also provided the voice of the computer on multiple Star Trek series. Her TV career stretches back to 1959, when she appeared on the syndicated Whirlybirds, a helicopter adventure series. The following year, she popped up in The Untouchables and Leave It to Beaver (pictured).

Image: NBCUniversal Television Distribution

9. Eddie Paskey

 

Paskey (Lieutenant Leslie) didn't have as robust a resume as his costars when he joined Star Trek in 1966. In fact, Paskey only had uncredited appearances on four shows before his big break on the classic sci-fi series. Those shows include Ben Casey, Gomer Pyle, U.S.M.C. (pictured), The Dick Van Dyke Show and Mission: Impossible.