- You may be looking for the real world actor.
John Barrowman was an actor who portrayed Jack Harkness.
Biography
While playing as Jack Harkness who was fighting Sao Til, David Tennant interrupted them reminding them that they were done with filming. After Tennant left, the two resumed playing around in the set. (TV: Untitled [+]Loading...["Untitled (Tonight's the Night)"])
Behind the scenes
John Barrowman portrayed himself in the untitled sketch [+]Loading...["Untitled (Tonight's the Night)","the untitled sketch"].