I presume you mean, "Why does Peter Graves have a last name different from James Arness, if they are brothers?"To increase one's chances of success in the notoriously fickle entertainment industry,...
What is the real last name of James Arness and Peter Graves, his brother?.
The birth name of Peter Graves was Peter Aurness.
i am also a graves and my research shows that we are either English or Irish, hope that helped.
Yes, Peter Graves died March 14, 2010.