One of the gunplas that I bought at Toronto Comic-Con.

The GAT-X303 Aegis Gundam is a prototype transforming commander's use mobile suit developed for the Earth Alliance. Designed with the X300 series frame, the Aegis transforms into a mobile armor that utilizes a cruise mode & a attack mode. It is armed with CIWS, beam sabers mounted on both forearms and feet, a beam rifle, a shield, and only in it's mobile armor form, a energy canon.

The Aegis was originally developed by the Earth Alliance's G Project in order to turn the war on their side against ZAFT. However, when ZAFT got word that the G Weapons were being developed in Heliopolis, a neutral colony owned by Orb, the launch a raid and stole four of the gundams, with the Aegis being stolen by Athrun Zala. Athrun would continue to use the Aegis following the raid until April 17 CE 71, where he would use the self-destruct function to blow up the Strike.

Though the Aegis' data would be used to develop the GuAIZ, Dreadnought Gundam, and the Regenerate Gundam, it's X300 series frame would later be used in the development of the Raider Gundam, and a later variant in the second war, the Rosso Aegis Gundam.