Steve McQueen first appeared as bounty hunter Josh Randall in an episode which served as the pilot of his own subsequent series, Wanted: Dead or Alive, a spin-off of Trackdown launched the following year. Both series were brilliantly acted half-hour adult programs filmed in black and white with interesting directors; Richard Donner directed three installments of McQueen's series. Series star Robert Culp wrote an episode for Trackdown called "Back To Crawford" (which co-starred his then-wife, Nancy).  Many installments were based on actual case files of the Texas Rangers, adding to the series' realism. 

Robert Culp's first directing job did not come until 1965, when he directed his own script "Court Of The Lion", for "I Spy".

Sam Peckinpah wrote an episode for Trackdown called "The Town."

Culp went on to greater fame in the TV series I Spy and the movie Bob & Carol & Ted & Alice, among dozens of other roles. Actors appearing on the show in single episodes included Vic Morrow, Strother Martin, DeForest Kelley, James Coburn, Beverly Garland, Michael Landon, and Lee Van Cleef. The series ran over 70 episodes from 1957 to 1959, was produced by Dick Powell's Four Star Television, and was itself a spin-off of Powell's earlier series, Dick Powell's Zane Grey Theatre.

Decades later, another CBS-TV series about the Texas Rangers, Walker, Texas Ranger, featured an episode called "Trackdown," possibly to pay tribute to the earlier Robert Culp show.

Thanks Jason Culp for the corrections!