He played Mr. Jonas in Gunsmoke, Coach Ossie Weiss in the sitcom Hank, and Reverend Robert Alden in Little House on the Prairie.

Greer's final film role was as the 108-year-old Paul Edgecomb, the character played by Tom Hanks in 1999's The Green Mile.

He was the major guest star as a man framed for murder in "Five Minutes to Doom" (1954) and as an eccentric millionaire in "The Superman Silver Mine" (1958).

[citation needed] He played the role of the marshal in the two-part "King of the Dakotas" (1955) and appeared as Ray in "Paper Gunman" of the NBC Western anthology series Frontier.

[5] In 1960, Greer appeared in the episode "Dark Fear" on the CBS anthology series The DuPont Show with June Allyson.

He would return for five more episodes, making him the most frequently cast guest actor of non-recurring roles on the series (tied with Richard Anderson).

In 1962, on the ABC/WB Western series Lawman, in an episode titled "The Unmasked", Greer was cast in a fictitious portrayal of Boston Corbett, the Union Army soldier who shot and mortally wounded Abraham Lincoln's assassin, John Wilkes Booth.

From 1992 to 1996, he tended to the spiritual needs of the townsfolk in fictional Rome, Wisconsin, as Reverend Henry Novotny in Picket Fences.

In the 1997 film Con Air, Greer appeared as an old man discovered hiding under a pick-up truck at "Lerner Field".

Most of Greer's approximately 700 movie and television appearances had been in supporting roles,[2] but he told the Albany Times Union in an interview in 2000, that "every character actor, in their little sphere, is the lead.