Somlum is a one-of-a-kind Lost Number Zoanoid and one of the three Lost Number Commandos in the Guyver series. He, along with his comrades Aptom and Dyme, were assigned to protect Richard Guyot following the destruction of Cronos Japan by the Guyvers Sho Fukamachi and Agito Makishima.
After the fall of Cronos Japan, the Lost Number Commandos accompanied Commander Guyot to the Makishima residence to meet with Agito to plot how to best eliminate Guyver-I. Agito, not yet aware that Guyot suspected he was Guyver-III, excused himself from the meeting and shortly after returned in Guyver form to try and kill Guyot. Somlum and the other Lost Numbers intervened and Agito was forced to withdraw in order to keep up his deception.
While Agito led a squad of Cronos troops to abduct Mizuki and Tetsuro Segawa, the Lost Numbers were sent after Sho as he and his new ally Masaki Murakami attempted to rescue Sho's father Fumio, who had also been kidnapped. During the fight, Somlum used his special bio-adhesive fluid to the team's advantage, fusing Sho's arms together. Mustering all of his strength and will, Sho forcefully tore his arms free, badly injuring himself in the process. With his arms free, Sho was able to use his Mega-Smasher and he vaporised Somlum.
Somlum's and Dyme's deaths would spur Aptom into a mad desire for revenge against the Guyver. The ultimate irony, of course, is that Aptom would later join the Guyvers in their war to overthrow Cronos.
In human form, Somlum appears as an Asian man with long grey hair and peculiar lesions on his forehead and temples. His zoaform appears to be a semi-humanoid reptile with green and purple skin (the purple patches are yellow in the OVA), an avian beak and warped, googly eyes. Fleshy tendrils under his beak and atop his head make him almost resemble a chicken. Unlike Aptom and Dyme, Somlum's zoaform is confined to a single shape like regular Zoanoids.
Somlum possesses great agility and reflexes. In battle, he uses these attributes to leap about wildly, easily evading most attacks and rushing in close to maul opponents with his razor-sharp claws. His signature weapon is a unique bio-adhesive fluid that he can use to trap foes. This "bio-glue" can merge with living organisms and become a part of them; in the case of the Guyver, Somlum used this glue to fuse the Guyver's arms together so he could not use his vibro-swords or Mega-Smasher. Sho was able to separate his arms again, but only by tearing apart his own flesh.