Kamen Vers

 was a human-Movellan hybrid, created in secret by the Movellans to be a weapon. He built the planet of Mto, so named after the woman who raised him as his "mother", from the debris of crashed spaceships. He planned to find the First Movellan, who he referred to as his "father", but was ultimately thwarted by the Tenth Doctor and Anya Kingdom, as well as his own mother, who was revealed to be none other than River Song in disguise. (AUDIO: The First Son)

Behind the scenes
The name Kamen Vers is an anagram of Mark Seven, who is later revealed to have been the First Movellan all along.