Agatio

Agatio is Golden Sun: The Lost Age's not-so-jolly green giant, and one of its main antagonists. He is one of Prox's great warriors, as well as a powerful Mars Adept. He travels with Karst, though he is introduced later, during the scene in Champa. Agatio is rather rash and prefers to keep on fighting even when the odds are stacked against him, which can be seen as a lack of intelligence rather than bravery.

In Golden Sun: The Lost Age
Agatio is from Prox and travels with Karst to search for Saturos and Menardi. Upon hearing of their defeat at Isaac's hands, they immediately seek revenge for the deaths of their comrades. He also wishes to have the lighthouses lit so that Prox will not disappear, but also says that their power will be restored, hinting that perhaps he and Karst were not only seeking to have their hometown saved.

Agatio is first seen in Champa with Karst and Alex and he is unimpressed by the look of Felix's party, doubting that they will amount to much. He even hints it might be better to take the Jupiter Star and Sheba from them. The group leaves without further conflict and are not seen until at Jupiter Lighthouse.

At Jupiter Lighthouse, Agatio and Karst attempt to take down Isaac and Ivan. They are successful in downing them, but Felix's party turns up, preventing them from taking their lives. Agatio wishes to keep fighting, but Karst persuades him not to, even though it was her sister Isaac killed, so they simply make sure Felix takes the Mars Star then go to the aerie.

At the aerie, Agatio and Karst get into a battle with Felix and Piers after taking the Mars Star, angered at them for saving Isaac. However, Jenna and Sheba arrive to help out, but Agatio and Karst continue to fight. No matter how the battle turns out, Alex turns up and the three escape on the elevator before Isaac's party and Kraden turn up.

The last time Agatio and Karst are seen, Alex is not with them and they have been transformed into Flame Dragons by the Wise One. Isaac and Felix's party do battle with the dragons in Mars Lighthouse, unaware that they are Agatio and Karst. After the battle, the two have no energy left to survive and are dying so Agatio hands the Mars Star to Felix, telling him to go and light the lighthouse, then the two await their deaths.

Fan influence
Agatio is rarely ever written about and usually only in fanfiction set during The Lost Age. He is possibly one of the least popular characters, since he gets so little attention from the fandom.