(written from a Production point of view)
O'Hanlon has also appeared on such television shows as M*A*S*H (starring David Ogden Stiers), Petrocelli (starring Susan Howard and David Huddleston), CHiPs (working with Michael Dorn, Jason Evers and Robert Pine), Magnum, P.I. (with Elisha Cook, Jr. and Kenneth Tigar), and the 1990s version of Fantasy Island (starring Malcolm McDowell and Mädchen Amick, with Olivia d'Abo and Richard McGonagle). In 1977, he had a recurring role as Ned Nickerson on the ABC series The Hardy Boys/Nancy Drew Mysteries, co-starring with William Schallert and, in one episode, Marc Alaimo.
During the 1989-1990 television season, O'Hanlon played Sergeant Rafferty on the CBS series Jake and the Fatman. The previous year, he had a supporting role in the acclaimed ABC mini-series War and Remembrance, which also featured Ian Abercrombie, John Rhys-Davies, Lawrence Dobkin, Walker Edmiston, Bruce French, Leslie Hope, Richard Lineback, Byron Morrow, Glenn Morshower, George Murdock, Charles Napier, abd William Schallert. In addition, O'Hanlon co-starred with Leonard Nimoy in the 1975 ABC Movie of the Week The Missing Are Deadly and with James Cromwell and Armin Shimerman in the 1990 TV movie Miracle Landing.
O'Hanlon's motion picture credits include Our Time (with Jerry Hardin and Meg Wyllie), The Evil (co-starring Andrew Prine), and The Karate Kid, Part II. He also had an uncredited role as Mr. Peter Myers, father of William Shatner-mask wearing serial killer Michael Myers, in the cult 1978 horror hit Halloween.
More recently, O'Hanlon appeared with Alice Krige in the 1999 biographical drama Molokai: The Story of Father Damien and co-starred with Joanna Cassidy in the independent film Moonglow. His latest role was in a 2005 episode of Lost, the hit ABC series co-created by Star Trek producers J.J. Abrams and Damon Lindelof and starring Daniel Dae Kim and Terry O'Quinn. The episode he appeared in, "Deus Ex Machina", was co-written by Lindelof and also guest-starred Kevin Tighe.