Mason is a prisoner aboard the Astral Queen and takes part in a prison revolt aboard that ship (Bastille Day).
Nothing is known about Mason's pre-holocaust life except that he was a prisoner aboard the Caprica-bound Astral Queen, on his way to have his parole eligibility assessed.
He seems to have an inferiority complex and is offended by Cally's lack of interest in having a conversation with him while she was being held as a hostage.
He later removes her from her holding cell and attempts to rape her. Cally bites a part of his ear off in self-defense and Mason responds by shooting her in the stomach.
In a rage from being bitten, Mason tries to kill Cally, but is slain by Captain Lee Adama before he has a chance.