Moff Gideon served as an officer in the Imperial Security Bureau, a law enforcement and an agency of the Galactic Empire. Following the Galactic Civil War he was thought to have been executed for committing a number of war crimes, but was found to have faked his own death and secretly built a small Imperial army after its downfall. Shortly after the war, Gideon stole the legendary Mandalorian lightsaber known as the Darksaber from its rightful owner, Bo-Katan Kryze, and oversaw the Great Purge, an Imperial attack on Mandalore that rendered the planet uninhabitable and led to the death of nearly all of its inhabitants.
After the destruction of the second Death Star, Gideon eventually began to take part in the Imperial remnants’ attempts to create clones that could be engineered to have Force powers. To achieve this end, he sought to obtain the Force-sensitive infant known as Grogu so that he could use the child’s blood, which had an extremely high concentration of midichlorians (the microscopic bacteria that give individuals the ability to use the Force).
Gideon demanded Grogu to be brought back alive and ordered cloning scientist Dr. Pershing and an ex-Imperial warlord known only as The Client to place a bounty on him. The bounty was collected on by Mandalorian bounty hunter Din Djarin, but the Mandalorian had a change of heart and took Grogu back, acting has his father.
This turn of events angered Gideon, who started overseeing the development of a third generation of Dark Troopers, which began as a variant of stormtrooper until the human was removed entirely. When Djarin eventually returned to his home planet of Nevarro to free it from Gideon’s remnant’s occupation, Gideon became personally involved.
Moff Gideon speaking to the Client before killing him.