I'll go with John Wayne. He's played a variety of roles and worked with a handful of classic directors and all that, but what makes him stand out from everyone else is that to this day he is synonymous with Westerns when noone else can make a similar claim about any another genre.
Leo might end up topping everyone by the time his career is up. He has worked with Cameron, Iñárritu, Nolan, Tarantino, Eastwood, Spielberg, Boyle, and is Scorsese's go to guy. Nearly everything he puts out is money in the bank and he's just slightly over 40.
Daniel Day Lewis might possibly be the best actor of modern times, but I don't associate "best actor" with "best career".