Yamada Nagamasa (山田 長政, 1590–1630) was a Japanese adventurer who gained considerable influence in the Ayutthaya Kingdom at the beginning of the 17th century and became the governor of Nakhon Si Thammarat province, which is on the Malay Peninsula in present-day Southern Thailand.

Its inhabitants were a combination of traders, Christian converts who had fled their home country following the persecutions of Toyotomi Hideyoshi and Tokugawa Ieyasu and Rōnin (unemployed former samurai) who had been on the losing side at the Battle of Sekigahara (1600) or the Siege of Osaka (1614–15).

He became involved in Japanese trade activities with Southeast Asia during the period of the red seal ships and settled in the Ayutthaya Kingdom (modern-day Thailand) around 1612.

Yamada Nagamasa is alleged to have carried on the business of a privateer from the period of 1620, attacking and plundering Dutch ships in and around Batavia (present-day Jakarta).

Furthermore, Yamada would have passed thousands of islands in the Torres Strait and Coral Sea and these would have provided safekeeping for any treasure and avoided a very long recovery voyage in the future.

He fought successfully, and was finally nominated Ligor (modern Nakhon Si Thammarat), in the southern peninsula in 1630, accompanied by 300 samurai.

After more than 12 years in Siam, Yamada Nagamasa went to Japan in 1624 on board one of his ships, where he sold a cargo of Siamese deer hide in Nagasaki.

The ship was released once the identity of the owner became clear, since the Dutch knew that Yamada was held in great respect by the King of Siam, and they did not wish to enter into a diplomatic conflict.