Juan Carlos I was King of Spain from 1975 to 2014, playing a crucial role in Spain's transition to democracy following Francisco Franco's dictatorship. His reign saw the approval of the Spanish Constitution of 1978 and he is remembered for preventing a coup in 1981.
This is based on winning 2 head-to-head matchups with other famous people, but also losing 22 head-to-head matchups.
Most recently Juan Carlos I of Spain lost a matchup to Kathy Bates (#844) voted by someone from United States.