Ōmura Sumitada was a Japanese daimyō lord of the Sengoku period. He became famous throughout the country for being the first of the daimyo to convert to Christianity following the arrival of the Jesuit missionaries in the mid-16th century. Following his baptism, he became known as "Dom Bartolomeu". Sumitada is also known as the lord who opened the port of Nagasaki to foreign trade.

The Sengoku period, also known as Sengoku Jidai is the period in Japanese history in which civil wars and social upheavals took place almost continuously in the 15th and 16th centuries. Although the Kyōtoku incident (1454), Ōnin War (1467) or Meiō incident (1493) are generally chosen as the Sengoku period's start date, there are many competing historiographies for its end date, ranging from 1568, the date of Oda Nobunaga's march on Kyoto, to the suppression of the Shimabara Rebellion in 1638, deep into what is traditionally considered the Edo period. Regardless of the dates chosen, the Sengoku period overlaps substantially with the Muromachi period (1336–1573).