The Unknown Man (also sometimes called The Hunter or, more derisively, Sunglasses) is an unnamed antagonist who was an operative in the service of Chief Kakuzawa.
Challenged by Kakuzawa to capture Lucy, he placed a sick wager for this task with Arakawa. He took the SilpelitNumber 28, mercilessly raped her, and then had operations performed on her to amputate her lower half in order to fit into a bag he carried around his back and had her hooked to technology to detect other Diclonii. In this condition, she would not last any longer than three days, being rendered mute and in excruciating pain. It is implied that he was also allowed to rape many other Diclonius girls, and was most likely a predatory pedophile.
Using Number 28 as a tracking device, he was able to locate Nana at the Maple House, but finally killed her in a fit of rage when she failed to find Lucy instead. He subdued Nana using a specialized crossbow firing a barb-spiked, poisoned iron ball into her gut, and then proceeded to attack Mayu and even Wanta. As his assault began, he even stooped so low to criticizing her appearance and taunting her concern for Wanta, who she feared to had been killed. His attempts to rape Mayu were stopped when she summoned Bando, who didn't bother to hide his disgust with this attacker, and whose mechanical parts were immune to his spiked iron balls. Despite being briefly surprised, Bando brutally beat him down. Ironically, Mayu herself stopped Bando from killing him, and he managed to escape. During a showdown on the beach, Lucy and Bando's fight was constantly interrupted by The Unknown Man's efforts, seeking to capture or 'protect' Lucy and avenge his beating at Bando's hands. Lucy finally killed him when he tried to shield her from Bando, and used his head as a projectile. His body and equipment apparently fell into the hands of Saseba, for the crossbow Bando took from him ended up in the hands of Saseba's top agent inside Kakuzawa's organization.
A monstrously sadistic predator reveling in the pain of other living things, The Unknown Man was also a clever, cunning, and deadly combatant who took delight in mayhem and murder. Nothing is known about his past or origin, but when Kakuzawa spoke with him of his plans for Diclonius supremacy, The Unknown Man referred to the new dominant species as 'We." This and the fact that he was so firmly in favor of the Diclonius race ruling the earth suggest he could have been a member of the Kakuzawa family, perhaps even possessing the vestigial horns most of them had. However, this cannot be confirmed.
Some fans of the series has spotted similarities between the Unknown Man and other characters, namely vicious trickster-demon Randall Flagg from the novels of Stephen King and Alucard, the monstrous warrior and predatory-minded vampire protagonist from Hellsing, a Manga made by Kouta Hirano, which like Elfen Lied, is ultra-violent.
In his brief appearance, high memorability, and specialized weapons within the series, Unknown Man can also be compared to Star Wars' Boba Fett, whose screen time in the first trilogy totaled all of ten minutes. Fett, though, is usually shown to have a deep sense of honor and morals, something Unknown Man obviously has no traces of.