The Boiling Rock was created relatively late during The War, by Fire Lord Ozai, who spared no expense in the construction of this prison.
After the war, the prsion was used to not only house the man who made it, but other Fire Nation War criminals as well. Soon, it started housing theives and killers, from not only the Fire Nation, but the whole world. There are currently hundreds of prisoners there. Of which more than half are convicted Firebenders. In all of its years of operation, nobody had ever escaped the prison, but once when the Boiling Rock was infiltrated by Sokka and Zuko.