Frank Johnson was 33 when his superhuman-strength powers manifested themselves for the first time. At first he didn't know how to control them and this had disastrous results. Everything he bumped into would be like a car hitting it. This also happened when he bumped into the walls of his house, causing it to collapse and killing his wife and daughter in the process. After the incident the Police tried to arrest Frank for the crime and he's been on the run ever since. Stricken with grief Frank worked as a fireman in New York for a while, trying to rescue people like he couldn't do for his own wife and child. After some time his heroic acts as a fireman where put on television and, because he was still wanted by the law, he left the job.
Monstro was created by Robert Kirkman and Khari Evans and first appeared in Amazing Fantasy Vol.2 issue 15 (2006).
Major Story Arcs
After some time Frank joined the Damage Control cooperation as a member of their Search-And-Rescue division. There he became good friends with fellow super powered heroes, such as the Visioneer and the Slaying Mantis (who was actually Eric O'Grady, the newest Ant-man, also on the run for the law).
Civil War and World War Hulk
When SHIELD found out that some of the members of the Damage Control team had powers, they were required to register with the Super-Human Registration Act. Frank obtained a fake I.D. with the help of Ant-Man in order to conceal his identity. Frank was one of the heroes who helped build op New York city after it was devastated by the Hulk and his Warbound during the World War Hulk events.