The comics describe that Leir dwelt in Avalon with other Celtic gods.

The books describe that when the Heliopolitan god Seth sought to make war against the other gods, he dispatched foul beasts to both Avalon and Asgard. Thor pursued a griffin-like beast through a dimensional rift to Avalon. When the Celtic gods saw Thor, they blamed him for the arrival of the beasts, and Leir battled Thor due to the misunderstanding. Hogun the Grim had followed Thor to offer his support. The three gods battled the beast and drove it off.^[1] Leir felt he owed Thor a debt for helping against the winged monster, and sent a force of Celtic gods, including Caber, to battle the armies of Seth when he attacked Asgard.^[2]

The books describe that Leir and Caber next attacked the camp of the Fomorians, the traditional enemies of Avalon.^[3] Leir and Caber later entered Asgard again through a dimensional portal. Leir attempted to claim Sif as his bride, but she said he must help rescue Thor, and battle her champion.^[4] Leir and Caber clashed with Heimdall in Asgard, and then accompanied Sif to Earth in search of Thor.^[5] Leir, Caber, and Sif then traveled to the Black Galaxy and found Thor there. The gods then traveled to Asgard, with Hercules. Leir, Caber, and Hercules then battled Ymir, and witnessed Asgard's victory over Ymir and Surtur.^[6] Leir then challenged Thor to a duel over Sif, believing him to be her champion, but was instead defeated in a duel with Sif.^[7]

The books describe that Leir has the typical powers of the Celtic gods of Avalon. This includes superhuman strength, speed, durability, stamina, and reflexes, and a drastically long lifespan.

Leir can generate electrical energy from his hands as a lightning-like spear, which he uses as a weapon. He also wields a shield of unknown properties.

Leir is a highly proficient hand-to-hand combatant, a good swordsman, and an expert at spear-throwing.

• Leir at The Appendix to the Handbook of the Marvel Universe
• http://www.marvel.com/universe/Leir