Arthur Douglas is an alien known as Drax the Destroyer. He is played by Dave Bautista in the movie.
Drax has various scarring patterns on his body with each having a specific story. His skin tone was changed from a bright green in the comics to a muddier grey to avoid visual similarities to the Hulk.
-Rocket Launcher -Two Daggers
Drax once had a wife and daughter until Ronan the Accuser murdered them. Ever since then, he was a dark, brooding murderer out for revenge on the evil one. He is also shown to have a soft side when he comforts Rocket over the loss of his friend.
Guardians of the Galaxy
Drax wanted to kill Gamora originally because her father, Thanos, played a role in the murder of his wife and daughter. However, Peter Quill convinces Gamora to trust Drax, and the two become good friends following their escape. At the end of the movie, Gamora reminds Drax that his wife and daughter are avenged now that Ronan is dead, but Drax tells Gamora that Ronan was just a "puppet" and Thanos is the real villain behind their deaths.