When Wayne Rogers quit the Korean War war comedy shortly before Season 4 (stemming from his dissatisfaction with Capt. “Trapper” John McIntyre’s sidekick status), Mike Farrell seamlessly stepped in as Capt. B.J. Hunnicutt, who proved to be a perfect new still-sipping swamp-mate for Alan Alda’s Hawkeye.

(Weeks later, Harry Morgan would show up as Col. Potter to fill a void left by McLean Stevenson’s Col. Blake, in another of the series’ A+ succession plans.)

https://tvline.com/lists/best-tv-characters-late-cast-additions-seinfeld-buffy-the-office/best-tv-characters-late-cast-additions-bj-hunnicutt-mash/