Serena Williams is a retired American tennis player, regarded as one of the greatest of all time. She dominated the sport with 23 Grand Slam singles titles and achieved a Career Golden Slam in both singles and doubles.
This is based on winning 21 head-to-head matchups with other famous people, but also losing 5 head-to-head matchups.
Most recently Serena Williams lost a matchup to Charles Bukowski (#1729) voted by someone from Austria.