Who is this person?

[J. Beckert]

That's it, Mick. He was at times part of the stock company at Ford's Theater. In March, 1865 he rented a room across the street at the Petersen house and came home to find Booth, who had come to visit him, taking a nap in the very bed that Lincoln died in.
I have a Ford's playbill from January, 1865 in which Booth's good friend friend John McCullough, Alice Gray, whose picture was found on his body, and Warwick all performed together in a production of The Robbers.