(written from a Production point of view)
Cassidy had previously appeared opposite fellow Star Trek performers Jean Simmons and Brent Spiner in the 1978 mini-series The Dain Curse. The following year, he and his "Shadowplay" co-star Kenneth Tobey guest-starred in an episode of Barnaby Jones, which also featured TOS performers Glenn Corbett and Lee Meriwether. He later co-starred with William Shatner, James Darren, Richard Herd, and Eric Server in a 1985 episode of T.J. Hooker.
Other television series he has appeared on include Falcon Crest (co-starring with Bibi Besch, Brett Cullen, Ellen Geer, and Robert Foxworth), Knots Landing, NYPD Blue (with Gordon Clapp and Sharon Lawrence), ER (in an episode with Clancy Brown, Eric Pierpoint, and Star Trek: Enterprise's Connor Trinneer), and Chicago Hope (in an episode with Scott MacDonald). His many TV movie credits include 1980's Reward (co-starring David Clennon, Lance LeGault, and Andrew Robinson), 1996's Innocent Victims (with J.G. Hertzler, Gregory Itzin, Don Keefer, Glenn Morshower, and Leon Russom), and 2000's Ali: An American Hero (with Casey Biggs and Clarence Williams III).
His only two film credits are Halloween III: Season of the Witch (1982, with Paddi Edwards), and St. Patrick's Day (1997).
Cassidy died on 26 August 2013 in Los Angeles, California, USA.