Itō Iga-no-kami Kagehisa, better known as lord Itō, was an ancient warlord of Mie and the founder of Itou family and eventually the Iga Clan.
His family had a tradition of training Kishu dogs to wield weapons and use fighting techniques. These dogs were called Ganin and they were used to protect Iga in war. Itō made a secret book of shinobi techniques and built a manor for his kin to use. His family trained shinobi dogs for generations.
Apparently, his family was originally allied with the owners of the Kōga ganins, but they became enemies when Kōga joined the enemy. Since then, Kōga has tried to steal the Itō's secret book of shinobi techniques.
Eventually, the human masters of the shinobi dogs died but the dogs kept on fighting as they obeyed the orders of their long-dead ancient masters.