In the 1950s, there were no "openly" gay actors. To make a public proclamation was unthinkable -- even a rumor could mean the end of your career.
Today agents, casting directors, producers, directors, and costars still encourage gay actors to pretend to be heterosexual -- at least until they're famous. Being "openly" gay will stall your career at the start.
Robert Gant was openly gay from the start. A practicing attorney, he broke into acting in 1994, with some guest spots on Friends, Ellen, Silk Stalkings, Popular, and Caroline in the City.
Mostly heterosexual or unspecified characters, but he played an iconic gay character in Queer as Folk (20002-2005): Ben Bruckner, college professor, partner of central character Michael (Hal Sparks).
And in Save Me (2007), he plays Scott, a resident of an "ex-gay" halfway house who starts a relationship with another resident, drug addict Mark (Chad Allen).
And in Kiss Me Deadly (2008), he plays Jacob Keane, a spy who happens to be gay -- probably the first "openly" gay action-adventure hero in movie history, and the only one to date.
There have been lots more tv guest spots since, on Hot in Cleveland, Bones, Mike and Molly, Baby Daddy, and Sean Saves the World. Sometimes gay characters, sometimes not. Sitcom casting directors don't seem to care who he's dating, as long as he has a square jaw, a muscular physique, and comedic timing.
Not a lot of movie roles. Maybe movie casting directors are still thinking "our target audience is homophobic, so.."