Dosan was a former priest and oil merchant, at the time Toshimasa. He then took the name of Hidemoto Nishimura and murdered Nagahiro Nagai who had protected him. He frequently made war with Nobuhide Oda but arranged the marriage of his daughter to his son Nobunaga Oda.
When his son-in law Nobunaga Oda embraced a new military technology he famously displayed on the occasion of a visit to his future father in-law in 1553. This technology involved of 800 ashigaru which came armed with long spears and 500 carried arquebuses. With this Dosan was much impressed.
When his adopted son challanged him, Dosan went to war and was killed.