Lord John Rossendale was a cavalry officer in the British Army. He was portrayed in the TV series originally by Alexander Armstrong, but later by Alexis Denisof.
Rossendale was originally a friend of Sharpe's, having helped him locate a missing regiment. However, he later engaged in an adulterous affair with Sharpe's wife, Jane Gibbons. He also used Sharpe's money to pay off his own debts. After Sharpe found out, Jane wanted Sharpe dead and challenged Rossendale to kill him on the battlefield of Waterloo. Sharpe confronted Rossendale in the woods, and Rossendale pointed his pistol at Sharpe, but did not have the courage to fire it. Sharpe took his pistol and sword and destroyed them. Rossendale lied to his comrades about his sword, claiming it was destroyed by French Hussars. He then vowed to kill Sharpe during the battle, but before he could even find Sharpe he was dragged off his horse by French riflemen and stabbed. He was somehow able to stay alive long enough, but a local woman who was among the looters killed him by slitting his throat.
Jane was pregnant with his baby by the time of his death.