Dr. Terminal was diagnosed with the fatal disease Einstein Syndrome. It devours the body, starting with the nervous system and ending with the brain. Dr. Terminal was only given two months to live. He defied this by creating a suit that fed the disease, keeping him alive. His first victims were the doctors who told him what he had.
Dr. Terminal was at one point arrested, but broke out of jail by eating the cell, bars, and a pot of carnations outside. His goal was to eat Finland, or stop the Umbrella Academy, whichever came first. Unlike many villains, Dr. Terminal knew he could not win. But he thought that also meant he couldn't lose.
At one point, he captured the Rumor, and ate her arm. The rest of the Academy saved her, and Dr. Terminal's fate was unknown.
Dr. Terminal is a skilled inventor. He can eat anything.
The Terminauts were created by Dr. Terminal as a contingency plan in case the Umbrella Academy ever reformed, even if Dr. Terminal had died or vanished. They wreaked havoc at a carnival on the day of Reginald Hargreeves' funeral.