The demon Amon is a major staple character in the Devilman. He rarely appears in the original manga series but has a looming presence throughout. His core character arc is that he is the demon that merged with Akira Fudo, transforming him into Devilman.
His character is rarely described other than being a mighty demon warrior but apparently also cared for Sirene. In later stories such as Shin Devilman or Neo Devilman his character is expanded. But it is not until the manga, Demon Knight that he is given an origin and a full appearance.
Amon's original human appearance resembled a light skinned male with messy black hair and dark eyes that featured markings coming down from those eyes. When on duty, he is always seen wearing black form fitting armor with a helmet that featured horns and small wings. He also featured spikes on his arms and a cape.
However after becoming a demon he grew far taller while still retaining his human appearance. His skin depended on the artwork with most being blue, turquoise, pale white, and least of all red with legs covered in black fur and a long thin tail with a spiked spade on the end. Amon has yellow eyes which depending on the story had black pupils or none at all. He had thin fangs in his mouth and large bat like wings in place of his ears with a bright red crest in the middle, he also had a pair of antenna connecting to the top of his head.
Amon being among the mightiest and strongest of the demons possessed a great and vast array of powers. Even before he gained his demonic appearance he was highly agile, intelligent, and strong. After his transformation, he gained the ability of flight through a pair of wings and his strength intensified. He possessed a vast array of psychic powers being able to detect those nearby and the strength of his enemies. He was able to extend spikes from his wrists that were able to cut clean through organic material which extended to his tail and wings. He could breath fire from his mouth, and fire off a powerful bolt of energy after it builds in power. He could extend his limbs and could breath under water. It is likely that these were only a portion of his powers.
Amon is by no means good and would at times kill someone with little retaliation; however, he was not evil. He didn't kill for no reason and would only do so when attacked or if someone stood in his way. He did show compassion for some people, the most notable was Sirene but in spite of what Sirene says about their relationship, Amon did not appear to have romantic interest in her only seeing Sirene as a close friend. Amon seemed to have a lover in the form of Nike, where his feelings temporarily surfaced from Akira Fudo, also implying that Akira's flirting and teasing with Miki was somewhat influenced by Amon given Miki's similarity to Nike.
Amon only appears in silhouettes and inside the mind of Akira Fudo in the original Devilman. However with much of his character and personality being explained and brought up, even at the birth of Devilman, it becomes clear that he was a incredibly powerful demon. It is later revealed that the demoness Sirene had loved him dearly even though the love was never returned to her. As with many others, Amon's original body was destroyed by God's attack on the demons, although he continued to exist as a non-corporal being requiring a host body to regain his physical existence. It is also hinted that he was placed in Fudo's body due to the will of Satan.
Whilst again not properly appearing he is however nearly resurrected when the demoness Nike, a past lover, Amon comes down to Akira and Amon's memories of their relationship come flooding into his mind, but Amon is stopped from returning when Nike is beheaded by Ryo Asuka.
In Demon Knight which takes place many years before the start of Devilman, Amon was originally a human knight and served the prince Lucifer alongside his companion Sirene and his pet dragon. One day, demons were spotted in the mountains and Lucifer and his knights were sent to deal with them. Slaying several demons, the group encounters a young girl named Yuria and her werewolf companion Urga. The groups came together to fight the demons but Amon, his dragon, and Urga got separated from the others. Amon and his group encounter Satan, the gestalt form of Lucifer, his pegasus, and Yuria. Amon questions what happened with Satan explaining that his/her form is evolution, proceeding to forcefully fuse Amon with his dragon and Urga, with Amon becoming a demon.
The events were seen by Akira in his dreams as he explains it to Ryo Asuka. Ryo however realizes this is actually Amon's memory, having had the same dream himself, including when Satan did the act to Amon.
Amon appears sporting high-tech armour fighting alongside Sirene and many other demons as well as Satan in space against the forces of God. However, Amon was pushed back with his memories inhabiting his armour. The armour would later be used by Yuki Fudo allowing the human to access Amon's powers and even make a mental connection with Amon. With reluctance and wanting to settle old scores with his more villainous rivals, Amon allows Yuki control of both the armour and the powers it gives him.
- In Shin Violence Jack, Jack is gradually revealed to be Amon. This incarnation has at some point betrayed demonkind to side with humans, like Devilman in the TV-series. He also references Satan, showing familiarity with him, although he does not appear within the narrative. Amon and the Skull King speak about each-other as old acquaintances, but he does not appear to recognize Miki Makimura. His appearance is a combination of the original Violence Jack design and Amon's human form from Akuma Kishi. At first he looks mostly like Violence Jack, but after entering hell he regains the signature marks under his eyes. When fighting Jinmen, Lyamon, Bau and Salamandra, he temporary reverts to his demonic form, but it is always in shadows or obscured by motion-effects. After defeating Skull King, who leaves with the other demons and Miki, he made sure to escape with Ushio, Miki Makimura and Sara, a young woman who became a Devilman after merging with Sirene.
Amon comes from several sources including the Ars Goetia demon Marquis Ammon as well as the King of Judah who was known for possessing an early god complex.