The Grand Serpent

His Supremacy the Grand Serpent was a political figure on Inston-Vee Vinder's home planet. True to his name, he had the ability to project serpent-like creatures out of his body before reabsorbing them, being part of a rare binary demi-species. He confirmed the Thirteenth Doctor that "the Grand Serpent" was not his birth name, but rather a title he had earned, many years prior to their meeting.

As part of a scheme in which he allied with the Sontaran Empire, the Grand Serpent, in possession of time travel, interfered in the foundation of UNIT in the 1960s under the name of Prentis and remained an important official within its hierarchy for subsequent decades, concealing his lack of aging through secrecy, doctoring paperwork, and occasion assassinations. He was finally found out in 2017 by Kate Stewart, just as he had finished arranging for UNIT to be disbanded by its international backers.

Biography
The Grand Serpent met the Alforia to discuss terms. Once the official meeting was concluded, he ordered Vinder to cease recording and then demanded the Alforia hand over five dissidents being sheltered in their territory to face trial, and for another four, all relatives of his critic Frey Sampor, to suffer a fatal accident. Inston-Vee Vinder reported the incident, resulting in him being reassigned to Observation Outpost Rose. (TV: Once, Upon Time)

He positioned himself on Earth in 1958 in order to assist the founding of a new organisation known as UNIT. In 1967, after being identified as an alien by General Farquhar, he began a streak of assassinating those who stood in his way. In 2017, he encountered Kate Stewart, informing her that UNIT funding was being cut. When she retaliated by threatening to expose his history with the organisation, he attempted to kill her by leaving a bomb in her house. Later, he ordered UNIT to prepare missile strikes against various Earth cities before informing the Sontarans, with whom he had struck a deal, that everything was ready for their invasion of Earth. (TV: Survivors of the Flux)