Allopta was a Time Lord.
He was second-in-command for Xenaria's expedition to break the time loop surrounding Planet 5 about 12 million BC, so the Fendahl could be released and used against the enemy. Like all members of the expedition, he had been changed into a Elder Thing as camouflage during the time period.
Investigators One and Two killed him and scanned his brain to learn more about what was happening. When they discovered he was a transformed Time Lord on a deep-cover mission, they each transformed into a copy of Allopta to infiltrate and learn more. (PROSE: The Taking of Planet 5)