If there was one star, other than Johnny Carson, who was a fixture at NBC for the bulk of his career, it would be Michael Landon.
After Bonanza, Landon branched out on his own with Little House on the Prairie, and followed that with Highway to Heaven, which lasted 5 seasons total (1984-9), the last as a mid-season replacement. Prairie co-star Victor French (ex-Carter Country) came along for the ride in what would be his last series. French passed away after production on the series had ended.
Jonathan Smith (Landon) is an angel sent to Earth to help people. Mark Gordon (French) befriends Smith and becomes his partner. They travel from city to city, adopting different identities and jobs to fit in.
Let's take a look at a sample episode, which reunited Landon with one of his former co-stars from Bonanza, Lorne Greene:
The 90's series, Touched by an Angel, worked along similar lines, perhaps helped along by the fact that one of its stars, singer-actress Della Reese, was also an ordained minister. Currently, Highway is airing on stations such as Retro and INSP.