Oda Nobunaga (1534-82) was the one of the most powerful daimyo in the late 16th century Japan. He brought Japan's central region under his control, but he was killed by Akechi Mitsuhide, who was the one of his senior statesmen, at the Honoji temple in 1582.
Nobunaga was well known as an enlightened lord and he had interest in European people visiting in Japan, their culture, and their trading items. As for christianity, he didn't reject the petition for the mission by the Jesuits and allow them to build churches in Kyoto and Azuchi.
This portrait is supposed to be painted in 1583 to commemorate the first anniversary of Nobunaga's death.