Had to be Son Goku from Dragonball. This guy is not just the strongest on earth, not the galaxy, not the universe, but the strongest in all 12 universes!! How crazy is that. Ok, maybe there are someone else who might be stronger than him like the great priest or Zemo. But Goku is the main protagonist of this anime and so he shall be regarded as the strongest anime character of all time. 

Outside of Dragonball, the other newer character is probably Saitama from One Punch Man. Saitama is designed to be the strongest character in this anime and he had even defeated an alien who claimed to had reigned over many galaxies out there. In that battle, we were told that Saitama did not even try hard enough. His signature move is always a single punch that is capable of defeating any enemy.

There are many other anime characters who are strong in their own ways. But all of those anime are set on Earth and so, I would say Goku, who had defeated all opponents from 12 different universe, is the strongest of all time.