The Invisible Man is a character from the Monsters vs. Aliens series.
Prior to the events of B.O.B.'s Big Break, in the 1950's, a male scientist tested out an invisibility serum which would last for an hour. He tried to play practical jokes on his colleagues, but unfortunately, timewise, the serum's effects were permanent, and he was taken into custody by the government. He found himself around a blue-colored blob called "B.O.B.", and they were the best of friends. Afterwards, after the facility gained a couple more monsters, he played practical jokes on them, too, even after his friends tried to escape. One year after, Insectosaurus was placed into the facility. The invisible man tried to play practical jokes on Insectosaurus, but the Missing Link kept him as far away from Insecto as possible. However, in 1984, a fatal heart attack cut the invisible man's funtime short, and he died in a chair. The other monsters lied to B.O.B., saying that he escaped, just so he wouldn't get upset.