User blog comment:HozzieHozzbourne/Strongest champion outside of the game/@comment-4915885-20130919212001/@comment-5557556-20130919221031

Yep, Karthus without any doubt. He is already dead, so he can't die, he can strike his foes from a very far distance, and with each soul consumed he becomes more powerful.

Imagine all the power that he has under the hood which he acumulated through all these years.

He is like Veigar in game who can stack infinite power.