Which actor has won the most Oscars?

Lots and lots and lots.

Throughout the past 81 years, accounting for ties and repeat winners, AMPAS has presented a total of 82 Best Actor awards to 73 different actors

Throughout the past 81 years, accounting for ties and repeat winners, AMPAS has presented a total of 82 Best Actress awards to 68 different actresses.

Throughout the past 73 years, accounting for ties and repeat winners, AMPAS has presented a total of 73 Best Supporting Actor awards to 66 different actors.

Throughout the past 73 years, accounting for ties and repeat winners, AMPAS has presented a total of 73 Best Supporting Actress awards to 71 different actresses.

In addition, actors occassionaly win awards as directors, producers and writers.