In the anime series Gundam Seed, the GAT-X303 Aegis Gundam is a command type mobile suit in service during the first half of Cosmic Era year 71. It is stolen by ZAFT pilot Athrun Zala on 25 January and serves as his mobile suit until its destruction in late May while fighting Kira Yamato in the GAT-X105 Strike Gundam and Tolle Koenig in his FX-550 Skygrasper.

The X303 Aegis is a commander-type mobile suit with very advanced sensors and heavy attack power (it is apparently named after the Aegis combat system, rather than directly for Zeus's shield). It can transform into a mobile armor configuration armed with a very heavy energy cannon (which is later mounted on the GAT-X131 Calamity Gundam). For close-range combat, Aegis is equipped with 4 beam sabers. As these weapons are mounted on the forearms and feet rather than hand-carried, all four can be wielded simultaneously, in either mobile suit or mobile armor configuration.

The Aegis Gundam is transported to Earth shortly after the Battle of Orbit on February 13 to pursue Archangel, it is held at Carpentaria Base in Australia until Archangel passes through the Indian Ocean, where it is sent to rendezvous with the Vosgulov-class submarine Cousteau. The Aegis, Duel, Buster and Blitz Gundams successfully intercept Archangel in midocean and force the heavily damaged assault ship to lay over at Orb for repairs.

Athrun self-destructs the Aegis Gundam while grappling the Strike Gundam, destroying both units. He ejects before self-destruction and is found injured on the shore by Cagalli Yula Athha. Later in that year, he returns to combat piloting the new, Aegis-derived ZGMF-X09A Justice Gundam. From June to the end of the war he pilots the Justice Gundam as part of the Clyne Faction, alongside Kira Yamato in the ZGMF-X10A Freedom Gundam.

We last see the Aegis Gundam as fragments of a destroyed mobile suit on the island where Athrun and Kira fought, the remains of this fallen metal giant finding their final, peaceful use as a playground for young children. A variation on its transforming system is used by ZAFT, on a much larger scale, in the ZGMF-X11A Regenerate Gundam.

Specifications

GAT-X303 Aegis Gundam

Manufacturer: Morgenroete, Inc/Earth Alliance
Users: Earth Alliance, Zodiac Alliance of Freedom Treaty
Unit type: prototype commander use transformable mobile suit
Head height: 18.86 m
Base weight: 79.9 t
Special equipment: Phase Shift armor
Powerplant: Ultracompact battery, sustainable delivery approx. 2-3 megawatts
Armament: "Igelstellung" 75mm multi-barrel CIWS x2, beam saber x4, 60mm beam rifle x1, "Scylla" 580mm multi-phase energy cannon
Pilot(s): Athrun Zala