Mark Sheppard is a British actor of Irish and German descent. Mark is best known for his guest spots on American television shows. Some of his most memorable roles were Badger, the cockney crime boss, on Firefly, Patricia Arquette's serial-killer nemesis, Dr. Walker, on Medium, Gaius Baltar's lawyer, Romo Lampkin, on Battlestar Galactica, as well as a stint during the fifth season of 24 as the villian, Ivan Erwich. In 2007, he landed a regular supporting part on Bionic Woman, as Dr. Anthony Anthros, the scientist who invented her "bionic" technology. Sheppard's resumé also includes appearances in such films as Boa, Evil Eyes and Broken.
In 2009 he scored a guest spot on Supernatural as the demon Crowley. Since then he has appeared in every season as sometimes ally and sometimes nemesis to the Winchester brothers.
He married his wife, Jessica, on March 6, 2004. They have two sons, Maximilian and William, and live in Los Angeles, CA.