As the head of the Amadeus Syndicate, he helps Morden to obtain new weaponry and also creating his own army. He is the final boss of Metal Slug 4. He controls the Amadeus Mother Computer, a three part contraption. After defeating him, the base begins to collapse while he is still stuck inside the last machine. It is unknown if he survived the destruction of the base.
Amadeus appears several times in Metal Slug Attack, both in Extra Ops and Another Story. Just like in Metal Slug 4, he is affiliates with Morden and his army. Amadeus is referred to as the Doctor, both by the characters and in-game.
In "Amadeus' Revenge" Extra Ops, he tests out a new Type γ Mother Computer and is delighted with the results. When confronted by the clumsy Rumi, he attempts to kill her with lasers, but she dodges them. She then throws grenades which seemingly miss, causing him to laugh. The grenades suddenly reappear again and explode, destroying the Mother Computer, though he survives, and is clearly not pleased.
In "Fall of Disaster", Amadeus is hesitant to abandon base due to an Invader attack spearheaded by Annette and Schwarz Metzelei, stating that if he left, he would have to wait years for his plan to get back on track. However, the two Invaders eventually leave after getting the desired results, although the syndicate has taken heavy casualties.
The Iron Fortress mentions him when White Baby gets damaged from Allen O'Neil's Red Sergeant Drill in "Protection of the Fortress".
Amadeus eventually develops the Sea Satan II. When two young children sneak into the facility, Amadeus unleashes his weapon on them, feeling remorse for having to kill children, but must do so to protect the secrecy of his weapon. Much to his surprise, the two destroy the Sea Satan II and he retreats, commenting on their strength.
He appears in Another Story in the chapter "Guilty Child", where Amadeus soldiers bring Abigail to him. He is initially confused by her aggressive stance, but when she and Allen O'Neil mention a little girl's voice, he becomes horrified after realizing the culprit. White Baby forcefully places him into a Mother Computer, though he is freed when the two officers destroy it. He explains White Baby to them and promises to assist them, though he is concerned for White Baby's well-being when Abigail states that she will destroy everything in Morden's path to world domination.
Sometime after the Professor destroys the Sol Dae Rokker, Amadeus and several researchers find its remains and fuse it into an anima form to take over the world. However, White Baby arrives and causes havoc, leaving Amadeus at her mercy. Amadeus states that he didn't design her to destroy humanity, which she attempts to counter by stating that the strong must control the weak. Amadeus explains that there are others stronger than her, something which the AI finds amusing. Navy and Vita soon arrive, due to the former wanting to destroy Anima to prove she is stronger than the Professor. After exchanging some insults, Navy destroys Anima. Amadeus comments that it will take thousands of years for Anima to be recovered, and states that the Professor wasn't just skilled in combat when Navy brags that she is better than him. This suggests that he used to be good friends with the Professor, or admired his talents.
Although Amadeus' personality is never shown during the main game, In Metal Slug 4, he unleashes a sinister, maniacal laugh upon seeing the player.
In Metal Slug Attack, he is shown as a caring figure. Not having any children of his own, he created various AIs to mimic them, as shown with White Baby and Iron Fortress as both are AI appearing as children, and has grown attached to them as a father figure.
- Amadeus reuses the sprite of Parker, the businessman/representative of a video game company who had his briefcase stolen by the player in Metal Slug 2/X.
- Amadeus and Invader Queen are only final bosses which have their own final boss theme.
- Amadeus has unused sprites of himself walking and smoking a cigar.