Undoubtedly one of DC's most alluring characters, the Martian Manhunter first arrived on the scene back in 1955. Surviving the destruction of his home planet, Mars, J'onn J'onzz was presumed to be the last of his kind (though future storylines would introduce other Martians). He arrived on Earth and aimed to help people.
Being a superpowered alien, some of J'onn's skills are incredibly similar to Superman's. But aside from the super strength and flight, he also has the ability to shape-shift, make himself invisible and he can even read minds.
These skills, along with his good-natured desire to protect Earth made him a valuable asset in the fight against evil and, as a result, he became one of the seven founding members of the Justice League.
Without a doubt, one of the most underappreciated characters in the DC Universe, it's nice to see J'onn getting more recognition these days (thanks to his prominent role on The CW's Supergirl). He is a noble warrior and one of DC's mightiest heroes.