Stenck was a Sontaran Commander who led an invasion of Earth in late 2021, seeking to exploit the final Flux event for the Flux Offensive. He worked with the Grand Serpent, who lowered the shields and allowed the Sontarans to invade. (TV: Survivors of the Flux)
When Stenck had captured the Thirteenth Doctor and Karvanista, he took pride in telling the latter that the Sontarans had all, but wiped out the entire Lupari race, in order to gain access to their ships surrounding the Earth. Upon hearing Karvanista's vow to kill every last Sontaran, Stenck laughed that he looked forward to the combat.
His plan to was bring the remaining Daleks and Cybermen to Earth, under a false peace treaty. Then he would manipulate the shield of Lupari ships around the Sontaran fleet to protect them, while leaving the Daleks and the Cybermen to be destroyed by the oncoming Flux cloud, and making the Sontarans the superior conquering race. But the Thirteenth Doctor and Karvanista tricked Stenck by manipulating the Lupari shield behind the Sontaran ships as well. Stenck was destroyed, with the rest of his fleet. (TV: The Vanquishers)