The phrase "undisputed number" means that something or someone is widely recognized or accepted as the best or most important in a particular field or category, without any doubt or argument. Full definition
Still undisputed number one for Arsenal despite a poor showing on his debut against West Ham, Petr Cech will be in the starting XI against Palace this weekend. (caughtoffside.com)
Almost every champion who wins the belt outright is rightly considered the clear undisputed number 1. (sbnation.com)
Michael was the undisputed number 1 driver in his teams for pretty much his whole career. (wtf1.com)