In Attack on Titan, who is known as "Humanity's Strongest Soldier"?

In One Piece, who is known as "Pirate Hunter"?

It's technically more of a "title" than a "nickname" but we'll run with it anyway.

*She's specifically referred to as "Frieren the Slayer" amongst demons, for just how many demons she's killed in her lifetime.

Can you guess the anime character just from their famous nickname? Let's find out!