Guy Gardner revealed to Kyle Rayner that Morro requested his duty as penance, as he killed his pets' mother in rage when he wrongfully thought it ate his brother (who was later found alive and well). His first act of atoning for his mistake was to adopt the creature's offspring as his own. Months later, after his brother's death (a natural cause) and the Sinestro Corps War, Morro chose to be the Corps' cryptkeeper.