His mother High Queen Silth was dying, but she refused to acknowledge it, having a god complex, and she ordered Gelltor and his siblings to go into Mossflower and steal treasures of beauty for her. Gelltor hated his mother and all his siblings, he just wanted a war with whoever lived in Mossflower and presumably desired to reign over and enslave those he conquered.
Gelltor first appears when the Wandering Noonvale Companions Troupe are stopping off in Mossflower and are having lunch. Gelltor and his sister Predak appear but, unlike Ascrod and Vannan who are somewhat civil to the squirrel Janglur, Gelltor is openly aggressive and insulting to the troupe. He takes offence at Florian the hare saying that if he doesn't like the soup, no need to be insulting, and then Gelltor makes to draw his axe but Florian drives him away. Gelltor and Predak apparently vanish without a trace due to the dark magic Marlfoxes are meant to possess.
When the Marlfoxes regroup, Gelltor votes for war. Mokkan shouts him down saying they came to steal not to start a war. Gelltor then takes a pack of water rats to break into Redwall in the early morning when all inside are asleep but he doesn't count on the warriors Janglur and Rusvul who are light sleepers who kill the invading rats, and almost kill Gelltor but he is only wounded. Here its proven Marlfoxes do not have magic power because Gelltor cowardly flees on all fours through the bush.
All the Marlfoxes berate Gelltor for his clumsy attempt, and at losing fighters. Gelltor is more angry and again votes for war but is shouted down. Mokkan suggests they capture a Dibbun, an Abbey infant. Even Gelltor likes this plan. Mokkan plans to use the captured infant as leverage to bargain for treasures. They capture Dwopple the infant mousebabe and plan to use him as leverage. To begin with, Gelltor debates Mokkan's competence and says mockingly "What you gonna do now, mister Stickabee?" and then Mokkan threatens to axe Gelltor if he doesn't shut up. However, they capture Dwopple successfully, and later meet the Redwallers at midnight the next night to bargain. Rusvul begins a battle against the Marlfoxes.
Gelltor fights dirty in the battle but when his sister Ziral is killed, Gelltor wants vengeance on her. Gelltor remembers Janglur's face because the squirrel was the one who killed Ziral. Gelltor begins to hunt down the Abbey dwellers. He tries one time to break into the Abbey grounds and actually succeeds with his water rats, but all his soldiers are slain and Gelltor is knocked out and bound as a hostage.
Rusvul and Janglur come up and taunt the defenceless fox. Gelltor scoffs at Janglur's "cowardice." This is his fatal mistake because Janglur politely offers the fox untied, and then to show he is not a coward he challenges the fox on one to one combat. Janglur says if Gelltor wins he is free to leave. An epic fight begins in the grounds between Janglur and Gelltor, although Gelltor is equal to the squirrel's strength, Janglur knocks Gelltor off his feet, then slices him in the head killing him. Gelltor's axe is put to use in the cellars chopping wood.
Out of all the Marlfoxes, Gelltor was the most warlike and arrogant. He did not get on with any of his siblings, although he was paired with Predak in scoutings. Gelltor especially did not get on with his brother Mokkan, who was more businesslike than warlike, and seemed to believe recklessness was the temperament of the fool. However despite all this hatred of his siblings he did not like to see them murdered, as the Marlfoxes had a code of honour, if one was killed they would be avenged. Gelltor was a very reckless and brave fighter, unlike many vermin, however his sheer arrogance would get his doom.