Giganto is the largest living thing in all the world. A behemoth whale creature summoned when the Horn of Proteus is used.
In Fantastic Four #4 - The Coming of the Sub-Mariner! Namor would call upon Giganto to attack the surface world and the Fantastic Four. Namor wanted to get revenge on the human race after his memory was restored by the help of Johnny Storm and discovered that Atlantis was destroyed. Namor blew the Horn of Proteus and summoned Giganto to attack New York. The Thing would strap a nuclear bomb onto his back and crawl into the mouth of Giganto while he was resting. The Thing set the bomb off and the explosion killed the creature.
Another Giganto would appear sometime later when Namor staged an invasion with some sea creatures and his friend Triton in disguise. It was called Project Revival and the plan was to stage an attack on New York which actually brought Susan and Reed Richards back together. Susan realized that she truly loved Reed and could not think of a future without him. Giganto would reappear sometime later when Captain Barracuda uses the Horn of Proteus to summon various sea creatures to attack the surface world. Namor and the Fantastic Four were able to defeat Barracuda and retrieve back the horn. Giganto would appear again when Llyron acted as the new ambassador of Atlantis and attempted to petition membership for Atlantis at the General Assembly of the United Nations. Giganto and other sea monsters attacked the United Nations building while Llyron was inside. Llyron's mother, Llyra blew the Horn of Proteus to make it look like Namor was responsible for the attack. Llyron would battle Namor in front of the United Nations and kill some of the sea creatures. Namor would accidentally rupture a gas main which ignited a huge blast and set Giganto on fire. Giganto would return back to the sea and Namor realized he was wanted for the attack on the United Nations.
The Pet Avengers
The Pet Avengers which included Throg, Lockjaw, Redwing, Niels, Ms. Lion, Zabu and Lockheed would fall into the ocean and placed in air pockets created by two sea turtles that are part of Namor's Loyal Honor Guard. The Pet Avengers are looking for the Infinity Gems and Throg senses two gems nearby. The sea turtles lead the Pet Avengers near the Great Beast which turns out to be a sleeping Giganto. The Pet Avengers are near Giganto when Niels starts to freak out in his bubble. The commotion wakes up Giganto and it ends up swallowing all the Pet Avengers. The Pet Avengers are safe and end up locating two gems inside of Giganto. Lockjaw teleports the Pet Avengers away from Giganto and back to dry land.
Powers & Abilities
Giganto possesses superhuman strength and durability. Giganto can spew water from his blowhole with enough force to snuff out the flame of the Human Torch. Giganto can attack his prey with the use of soundwaves called echolocation.