Merrick

Merrick was one of two hundred Wraith who were turned into humans by the Iratus bug retrovirus. He and the others were transported to a planet without a Stargate, as a means of preventing them from leaving. The Atlantis Expedition told them that they were suffering from a plague that caused memory loss, but Merrick was one of the few (roughly thirty) human-form wraith that realised something was wrong. These few managed to get together and form a plan, veen though they were getting daily doses of retrovirus. Merrick was one of the few who Lathan tried to convince to attack the soldiers and take their ship, and perhaps one of the ones who later helped Michael to kill Lathan after he ran away trying to prove that something was wrong. It is unknown if Merrick survived when Dr Mckay fired on the planet from above with a hive, but if he did, he might have been killed by the wraith hive that the human-form wraiths that had begun converting back into wraith had summonned. This is probable as Michael tells Teyla later that year that he barely escaped that hive with his life because they sensed the human in him.(ATL: "Misbegotten", "Vengeance")

Behind the scenes
Merrick probably had a strong mind, as Michael tells Dr Beckett when he captures him that the weaker minds among the human-form wraith stayed that way. (ATL: "Misbegotten")