In 2014 it was Aron Baynes. In 2015 it was Klay Thompson.
He didn't have the greatest series, but Klay Thompson is an NBA champion.
Thompson started all 6 games, playing an average of 38 minutes a game. He was questionable heading into the series, after suffering a nasty looking shot to the head in the final game of the Western Conference Finals. But, thanks in part to a week long break, Thompson cleared concussion tests and was ready to go for game 1. He scored an average of 16 points per game in the finals, below his regular season average of 21.