The man who would become Madcap was a religious person belonging to a group that organised a trip. This man, his parents and his sister Katy went to the trip in a bus, with some other forty people.
Terrorist scientists from AIM were trying to destroy a chemical developed by themselves, Chemical X07, which apparently included enzymes to incite a rapid healing in human bodies. The accident killed all of the people in the bus, except for the man who would become Madcap. Coincidentally, this man laid unconscious for hours on a pool of X07, which would eventually evaporate. He would recover consciousness in a hospital, but then discovered that he was the sole survivor and his faith in a rational universe collapsed. He ran away from the hospital and threw himself to a car trying to commit suicide. To his surprise, he was unharmed and felt no pain at all. This drove him completely mad. He correctly suspected that the accident had given him this immunity to damage, but could not understand why he was to obtain power from an accident who had killed forty people, including his family and friends.
Finally, he decided that things happen without a reason, and that nothing has a purpose. He soon discovered his other power, which allowed him to drive people crazy. He bought a bubble gun in a general store and stole a harlequin costume. He called himself the Madcap and wandered through New York City driving people crazy. He had no compunction about putting people in danger: As he could not be hurt, he could not understand that other people could be hurt.
During one of his first trips, he met newbie adventurer Nomad, who was at that moment Captain America's partner. Nomad befriended Madcap trying to understand his origins, motivations and powers. However, Madcap began to threaten lives, Nomad was forced to knock him out and overcome him.
Madcap was sent to a psychiatric hospital, but he used his powers and became the host of The Mystery Hour of Madcap in New York TV. Madcap found child super heroes Power Pack and tried to convince them to live adventures with him, but Madcap's adventures became dangerous and Power Pack left him. Madcap moved away, dancing and singing about the fun of further adventures.
A further encounter with Dr. Karl Malus led to Madcap accidentally touching one of Malus's inventions and, for the first time in a while, the Madcap could be hurt and feel pain. It is unclear which of Malus's discoveries led to this. Madcap left trying to find Malus, but he would lead his search through unusual methods, thus probably he would not find him. Malus is not aware of Madcap's search.
Shortly before the Secret Invasion, Madcap ran into Deadpool on a rooftop while the Merc with a Mouth was attempting a hit on Matt Murdock. A short quarrel between the two where they compared healing factors and a failed attempt to drive Deadpool insane that proved to have an opposite effect lead to a battle with Daredevil and Thor. Thor electrocuted the pair while they were holding each other and when they regenerated, only Deadpool seemed to survive. Madcap lived on as the white caption box present until after the conflict between the Avengers and the X-Men, where similar circumstances and some help from Luke Cage and Thor split the pair apart once more.
Emotional Control: Madcap has a specialized form of mind control that makes targets behave as if they were happily crazy for a few minutes - which can lead them to dangerous situations. Even if the target resists, he is still affected and cannot perform at his usual level. To use this power, Madcap must have visual contact with his target (Notice that he uses flashy clothes and a bubble gun as a weapon, all of which attracts attention).
Enhanced Human Regeneration: Madcap heals at top speed and recovers his vitality and stamina quickly. He cannot be killed or even stunned. He tried many suicide attempts, but failed, as he was able to survive each and every injury.
Virtually Indestrucible: Madcap is virtually invulnerable to all forms of attack, no matter how painful it may have become.