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Cai Qian was born in Tong'an District, Fujian Province, China. Facing starvation, he became a pirate in 1794. At the height of his power, he and Cheung Po Tsai commanded hundreds of ships and thousands of pirates; he was Tsai's mate. They predated others on the seas of Fujian, Guangdong and Taiwan Strait and came to be considered a major threat to Chinese political stability. Because the British businessmen sold English guns to Tsai, the Qianlong Emperor became angry with the British. The Qianlong Emperor blamed George Macartney over this issue, leading to Chinese hostility towards the United Kingdom during the Chinese Rites controversy. In 1799, Cai married a weapons expert who spoke English. Her expertise may have been beneficial to their accumulation of wealth. Some diaries say her name was Lin Yuyau (林玉腰) and that she had lived in Fangyuan, Changhua, Taiwan.
In 1802, Cai occupied Xiamen's guns bases.
In 1804 and 1805 Cai and Tsai twice attacked Taiwan's provincial capital of Tainan but were defeated. In the battle of 1804, Tsai defeated the Qing fleet from Wenzhou. Within the next four years he fought many battles against Tsai and Cai, vowing to destroy their fleets.
In January 1808, Fujian and Zhejiang admirals nearly destroyed their fleet near Hong Kong through a battle which lasted one day and night. They succeeded in defeating their enemies, causing Qing's navy to begin fearing Tsai and Cai. Cai committed suicide by shooting himself with a golden bullet. It is said that Cai had a great treasure which was hidden on Matsu Islands: it had never been found to this day.