A ratcatcher loyal to Prince Daemon Targaryen and the Black Council, Cheese as the history books remember him, was hired by Lady Mysaria, on the prince's behalf, to assassinate one of King Aegon II and Queen Helaena's two young sons.
With a vast knowledge of the hidden tunnels underneath the Red Keep, both himself and Blood breached the castle undetected. Breaking into the far less fortified Tower of the Hand, he took the Dowager Queen Alicent hostage. They were fully aware that the young Queen and her children visited their grandmother each evening, laying in wait for their quarry to approach.
While Blood murdered Helaena's guardsman, Cheese grabbed two-year-old Maelor, demanding that she choose which of her two sons they would kill. Explaining his contract, "a son for a son", he warned the queen to make her choice quickly, since his associate was more than willing to sexually assault her daughter and kill all three of them.
Upon hearing her answer to murder Maelor, he mockingly told the youngest child of her wishes, before Blood decapitated Prince Jaehaerys instead, much to Helaena's despair. True to his word, they left the others alive, though traumatised, taking the head with them as proof of the mission's completion.
Though Aegon ordered every rat catcher in King's Landing to be hanged, thanks to the evidence provided to him by the captured and tortured Blood, Cheese escaped punishment, going into hiding.