Marth is childish and jovial. However, when he needs to be serious, he can be gravely so. Marth is very protective of his friends, and will not allow harm to come to them. He seems to care about them more than he does himself; willing to sacrifice himself when needed.
During the events in Geomorph City, Marth was one of very few Geomorphs to escape Cadmus, and be free. His freedom was momentarily cut short by Cadmus officials, when they hunted him down. He was saved by the combined efforts of Firestormblaze and SaberX.
'Marth' is a corruption of 'Mars,' the Roman god of war. However, their personalities are not similar, as the god Mars was uncontrollable and violent, whereas Marth's character is more suited to a child, or loyal pet.