Marco was a cleric who went to Alfava Metraxis to hunt a Weeping Angel. His torch flickered when the Angels interfered with it and he warned Father Octavian. He was later surrounded by the Angels with the other clerics, the Eleventh Doctor, Amy Pond and River Song. (TV: Time of Angels) He was put in charge by Octavian to look after Amy. He sent three clerics to investigate a glowing light in the Byzantiums oxygen factory. He forgot about their existence when they were absorbed by the time field and went to look for himself, leaving Amy alone. He was erased from existence. (TV: Flesh and Stone)
When Rory Williams was erased by a time field, Amy remembered that she could still remember the clerics, even though they could not remember each other, in the hope she could remember her fiancé. (TV: Cold Blood)