Rodney Lange is the no-good younger brother of Iris, a woman who attracts the romantic interest of an immortal. (Iris works in a bar - unfortunate, since Rodney has that drinking problem....)
The episode description, from the official Highlander web site:
THE FIGHTER, #93211
Written by: Morrie Ruvinsky
Directed by: Peter Ellis
Guest Cast: Bruce Weitz (Sullivan), Wren Roberts (Belcher), Cali Timmins (Iris), Nicholas Lea (Rodney)
MacLeod's old friend Tommy Sullivan is a scrappy little Irishman, a one-time boxer turned trainer, who can charm anyone into anything. He charms MacLeod into backing his current boxer and charms Charlie into playing Cyrano to help him woo a shy waitress. But when a rival manager who was trying to steal Sully's fighter turns up dead, MacLeod's opinion of his old friend begins to be altered forever.
Nick was also in the episode "Money No Object," playing a different character.