Who is Pembroke Howard from Pudd'nhead Wilson and what is their importance?

Judge Driscoll's best friend, Pembroke Howard, is his second when he challenges Luigi to a duel. Pembroke arranges the duel, stands by while the two men fire guns at each other, and witnesses Judge Driscoll's will when he decides to write a new one before the duel. Only Pembroke is aware of the new will, and Tom is still the sole heir. Tom, however, overhears their conversation and is aware the new will has been written.