Whenever I would call for an appointment, whether it was a job or an apartment, and I would give my name, there was always that hesitation and when I'd get there, it was always gone. So I thought, I got enough problems trying to get an acting job, so I invented Martin Sheen. I've never changed my name; it's still Estevez officially.
[on changing his name] I never changed it officially. I never will. It's on my driver's license and passport and everything: Ramon Gerard Estevez. I started using Sheen, I thought I'd give it a try, and before I knew it, I started making a living with it and then it was too late. In fact, one of my great regrets is that I didn't keep my name as it was given to me. I knew it bothered my dad.
http://www.imdb.com/name/nm0000640/bio
While continually auditioning for shows, Sheen worked at various odd jobs and changed his name to avoid being typecast in ethnic roles. "Martin" was the name of an agent/friend, while he chose "Sheen" to honor Bishop Fulton J. Sheen
starpulse.com/Actors/Sheen,_Martin/Biography webpage no longer exists