Cornello is a low-rate alchemist and a fraud. He uses what he thinks is the Philosopher's Stone to fool the people of Lior into thinking that he is sent by the Sun God Leto with the power to perform miracles, including resurrecting the dead. Although he uses alchemy to bring prosperity to the desert city, his true intention is to convert the citizens into a fanatical army. The Elric brothers expose him for a fraud, and shortly afterward the incomplete Philosopher's Stone becomes unstable and shatters as it tears his arm into a mass of flesh and metal.
After the Elrics undermine his plan and Cornello is no longer of any use to the Homunculi, he is consumed by Gluttony. Envy, disguised as Cornello, maintains the deception until Lior is subjugated by the State Military. In the manga, Lust tells Gluttony he'd be better off not eating a fourth-rate fraud like Cornello, and kills him herself. Gluttony eats Cornello's dead body afterwards, Lust replying to Gluttony rather annoyed "I thought I told you not to eat that".