Groot
Groot is a sentient tree-like creature from outer space who first appeared as an invader. He can only say the repeated line "I am Groot", but it has different meanings. In the Marvel Cinematic Universe, Star-Lord, Thor, and Rocket Raccoon are able to understand him.
Groot was reintroduced as a heroic, noble being in 2006, and appeared in the crossover comic book storyline "Annihilation: Conquest". He went on to star in its spin-off series, Guardians of the Galaxy, joining the team of the same name.
Groot has become a pop culture icon, with his repeated line "I am Groot" becoming an Internet meme.