A promising biochemistry student at the University of Padua, Monica heard of the work of another physicist named Bruce Banner and sought him out. She met him in New Mexico and struck up a relationship which she used to steal as many secrets from him as she could. She would use this knowledge to win the Nobel Prize for her work in antitoxins.
She became disillusioned with the ways of the west and decided instead of working to heal people, she would instead concentrate on killing them. Her work on stopping toxins also made her the leading mind on the causation of poisons and stopping of antibodies, thus she implanted several children including her own daughter Carmilla Black(aka Scorpion). On her 16th birthday she sought out A.I.M. as she was programmed to do, but her daughter was already contacted by S.H.I.E.L.D.
When M.O.D.O.K. killed a scientist supreme, Monica assumed his position, and became leader of a cell away from M.O.D.O.K.'s control. She's made several attempts to seize power and enhance the size of her A.I.M. cell, but each time she was stopped, first by her own daughter and secondly through a betrayal by her old lover M.O.D.O.K.
Most recently she tried to recruit Barbara Morse (aka Mockingbird), which was thwarted by herself and Barbara's ex-husband Ronin.
Monica Rappaccini possesses no superhuman powers of her own. She is a genius-level biochemist and an authority on biological toxins. She is likely to be able to employ a wide range of A.I.M. technologies. She wears a phasing belt that allows her to teleport short distances.
House of M
During House of M, Monica worked alongside the Hulk and Carmilla Black to overthrow Exodus' government in Australia. While the Hulk governed Austrailia, Monica secretly worked on a program to create a cybernetic army to challenge the Earth's mutant rulers.