Professor Achilles Milo was a great chemist who turned to the dark side. He was one of Batman's foes and attempted several times to effect Batman with some sort of gas or drug. He's given Batman a drug to make him fear anything bat-shaped, and tried to make suicidal with a gas compound.However Dr. Milo was driven insane by being exposed to some of his own chemicals, and Batman sent him to Arkham Asylum. Where Batman actually sought out his chemical genius when he needed help. Another appearance was in Arkham Asylum: A Serious House on Serious Earth, where he was apparently cured of the gas, but no one would believe it. Elongated Man later confronts Professor Milo and looks to have his lower legs cut off and is now in a wheel chair. This is in fact a disguise as Milo is hiding the Silver Wheel of Nyorlath.
When Batman begins to hallucinate it is found that a past encounter with Milo's gas made Bruce Wayne create a more ruthless Batman person. The Batman of Zurr-Enn-Arrh was a back up personality that would take over in an event that Bruce Wayne was psychologically attacked leaving Batman out of action.He appears as the head henchmen of General Immortus. He grants superpowers to Immortus's minions and manipulates the pain receptors of Immortus's lesser minions.
Milo internalized The Human Flame's ability to create fire,removing his need for his suit and flamethrowers. The Human Flame overcomes his manipulated induced pain through sheer will power, injures Immortus, and tortures Milo into directing him to S.T.A.R. Labs for experimental treatments. Immortus leads Milo to rethink their strategy causing Milo to leave and venture out on his ownHe goes freelance and enters into a contract with Arthur Pemberton to heal the brain damage inflicted on his daughter; Lorna, in a battle with the JSA.
Batman: The Animated Series
Professor Milo first appears in the episode, "Cat Scratch Fever" playing the role as a Gotham City Villain who is hired by the names of Roland Daggett to produce a plague that would infect all stray animals in the city. He later appears in another episode "Moon of The Wolf" where he was a mastermind of the creation of an untraceable wolf-enhancing steroid hormone, as Anthony Romulus being his first test subject.
Justice League Unlimited
Dr. Milo then appears in a new series, Justice League Unlimited from the episode "The Doomsday Sanction", who is a member in a lab experimentation of genetic engineering project also called, "Project Cadmus". After a failed experiment gone bad, Amanda Waller, leader of the top secret project authorized to expel him from the experiment. Instead, Achilles Milo proceeded to release Doomsday in return to "get rid of the problems", but alternatively Doomsday slaughtered Milo, leaving him dead.
Batman: Brave and the Bold
Milo is seeen in a teaser. Milo trained numerous rats to steal diamonds across the city for him, and Batman teams with The Specter to stop him. After quickly defeating him, Batman tells Specter it's better to fight with mercy than vengeance. He then swings away. With Batman gone, Spector gazes down at the bound Milo. He then turns him into solid cheese and releases all the rats he controlled, enjoying his screams as he flies away.