The Trowa we know isn't the real Trowa. The real Trowa was shot by a soldier from earth. So the Trowa we know offered to be the new Trowa and pilot Heavyarms. He said he became fond of the Gundam and had the ability to pilot it so they let him. From that point on he was Trowa Barton. He is from Latin and pilots three Gundams, Heavyarms and Heavyarms Kai through GW Series, and Heavyarms Custom and Serpent in Endless Waltz.