The First Assistant was one of the Elders assisting Senta in draining life energy from the Savages.He prepared Nanina for transference and was left to oversee the process when Senta had to leave the laboratory to deal with an intrusion by Dodo.He nearly lost control, having to call Senta for help and taking more energy than usual, and afterwards was responsible for guiding Nanina outside the city.
He was on duty still later on when Edal ordered Senta to extract life energy from the First Doctor and assisted with the process.Afterwards, he took the Doctor to his guest room.(DW: The Savages)