Sakuma Morimasa (佐久間 守正, 1554 – July 1, 1583) was the son of Sakuma Moritsugu, cousin of Sakuma Nobumori, a prominent Oda retainer to Oda Nobuhide and Oda Nobunaga. Morimasa was born in what is now Shōwa-ku, Nagoya (situated in contemporary Aichi District, Owari Province), He was a retainer of Shibata Katsuie and one of his top generals in many of his campaigns. Morimasa was given the former Ikko Sect fortress Oyama Gobo in the Kaga prefecture by Oda Nobunaga; the fortress was subsequently named Oyama Castle in 1580 but went on to become Kanazawa Castle. After several campaigns in which he had fought, he was given the nickname onigenba which literally means "Demon Genba", Genba being his middle name.
After the betrayal of Akechi Mitsuhide which led to the death of both Oda Nobunaga and his heir Oda Nobutada, Morimasa sided with Shibata Katsuie over making Oda Nobutaka (the third son of Nobunaga) as heir to the Oda clan whereas Hashiba Hideyoshi (later Toyotomi Hideyoshi) supported Lord Sanboshi. Sanboshi was the heir to Oda Nobutada and was still an infant at that time. This argument led to the split of the Oda clan retainers into the two main factions led by Shibata Katsuie and Hashiba Hideyoshi.