Ghelmer is a demon and an antagonist in Devilman. He fights Devilman in an attempt to help Sirene in the fight against him. He looks like a giant slug-like demon and has the power to make it rain and has power to control water.
He attacks a nude Miki Makimura while she is taking a bath and tries to drown her. Miki is saved by Akira Fudo and he takes her to her room. He tricks Miki into drinking the water from his body and possesses her until Akira gets her to puke up the water. Gelmer confronts Akira once more in Miki's room but Akira chucks a blanket on him and sets it on fire to evaporate the water in him and weaken him. After beating him up, Akira guts him by penetrating him with his fist and Akira snaps his neck, killing the demon and leaving behind a watery corpse.
CB Chara Go Nagai World
In here, He captures Miki Makimura while she is asleep and brings her back to the glacier in part of Sirene's plan get Akira. Gelmer dresses up as Miki Makimura to trap Akira Fudo but freezes in the glacier and has to be defrosted by Akira's Powers(like how he set him on fire in Devilman). Akira says that he will unfreeze Gelmer if he tells him where Miki is. After being unfrozen, Gelmer says he won't tell and that he didn't agree with Akira's deal(since Akira decided that on his own). He gets into a verbal fight with Akira and Akira transforms into DEVILMAN!!!!! as they are about to fight, Sirene comes in and her DD cups distract Akira. As Akira and Sirene talk, He sits down and says that he can't stand it. It is then revealed that Miki was part of the Gelmer bait plan to pull a Maury (povich(you are NOT the father)) and find out if Akira was cheating on her with Sirene.