Karl Friedrich August Gützlaff (8 July 1803 – 9 August 1851), anglicised as Charles Gutzlaff, was a German Lutheran missionary to the Far East, notable as one of the first Protestant missionaries in Bangkok, Thailand (1828) and the first Lutheran missionary to China (1831-1848). He was a colorful "swashbuckling Pomeranian" who combined his prodigious talent as a prolific Christian author and linguist with participation in the illegal opium trade in 1830s China. He was one of the first Protestant missionaries in China to dress in Chinese clothing and was said to be so proficient in Chinese language and culture that he could pass as Chinese. His books were widely read and his adaptation to Chinese culture served as a model for the later work of missionary Hudson Taylor, founder of the China Inland Mission. In recognition of his travels, often illegal by Chinese law, up and down the Chinese coast, he was elected as a member to the American Philosophical Society in 1839. Controversial during his life, Gützlaff has continued to be so for historians.

During the First Opium War (1839-1842), Gützlaff served as an interpreter for the British government. Afterwards he became a magistrate in Ningbo and Zhoushan and the Chinese Secretary of the British administration in Hong Kong.

Karl Gützlaff was born in 1803 in Pyritz (present-day Pyrzyce), Pomerania, the son of a tailor, Johann Jacob Gützlaff. He was a brilliant student and his abilities with languages and knowledge of geography brought him to the attention of King Frederick Wilhelm III of Prussia in 1821. The king arranged for him to attend the Mission School of theologian Johann Jänicke in Berlin. After completing the school, Jänicke arranged for him to join the Netherlands Missionary Society for a three-year training course in Rotterdam. The Netherlands Missionary Society sent Gützlaff to Batavia (Java) in 1826. Subsequently, he moved to Singapore where he learned Chinese. Gutzlaff relocated to Bangkok in 1828 where he worked with missionary Jacob Tomlin of the London Missionary Society on a translation of parts of the Bible into Thai, Cambodian, and Lao. However, his main interest was the Chinese language and converting the Chinese to Christianity. He left the Netherlands Missionary Society in 1831, became an independent missionary.

Gützlaff was married three times to three English women. He made a brief trip to Singapore from Bangkok in December 1829 and married an English missionary, Maria Newell. He returned to Bangkok with his wife in February 1830. However, Maria died giving birth to twins in 1831, leaving a considerable inheritance to Gützlaff. Both children soon died. Gützlaff married again in 1834, this time to Mary Wanstall. The second Mrs. Gützlaff ran a school and a home for the blind in Macau. She returned to England in 1839 due to the threat of Civil War but eventually came back to Asia and died in Singapore in 1849. His third wife was Dorothy Gabriel who he married in Europe in September 1849 on a visit there. She accompanied him to Hong Kong in 1851 where he died that same year. Dorothy wrote a biography of him and lived until 1888.

In the late 18th century, the Chinese government had closed all of China to visits or trade by foreigners except for Canton (modern Guangzhou). in June 1831, Gűtzlaff violated that prohibition on his first visit to China, traveling up and down the coast by sailing ship as far north as Tianjin and defying Chinese government edicts. He spoke Fujianese (a Chinese dialect) fluently and wore Chinese dress.

In November 1931, he took up residence in Macau and later in Hong Kong. In 1832, along with East India Company staff Hugh Hamilton Lindsay, Gutzlaff joined a six-month long clandestine reconnaissance by sea that visited Amoy, Fuzhou, Ningbo, Shanghai and the Shandong coast. In late 1833, he acted as naturalist George Bennett's Cantonese interpreter on his visit to Canton. In these visits to Chinese cities, Gützlaff served as a translator, interpreter, and medical doctor. One of the purposes of these trips was to open China to trade with Britain. While it failed at that, Gützlaff's book, published in 1834, titled Journal of Three Voyages along the Coast of China in 1831, 1832 and 1833 excited interest in expanding trade with China. Gützlaff's book furthered the opinion that China, if pressed hard, would yield to demands that trade be allowed. He also suggested that violence could be useful to help traders and missonaries achieve their objectives. Gützlaff said, "[W]hen an opponent supports his argument with physical force [the Chinese] can be crouching, gentle, and even kind."

Gūtzlaff's experience and expertise attracted the interest of Scottish traders William Jardine and James Matheson in Canton. Britain had, at the time, a trade deficit with China. The British purchased large quantites of Chinese tea but the Chinese had little interest in purchasing any British products -- except opium which was grown in British India. Jardine and Matheson hired Gützlaff as an interpreter on its opium trading ships clandestinely plying the China coast. They agreed that Gützlaff could distribute Christian literature while on the opium voyages, inspiring the wry comment that while the opium dealers distributed opium off one side of the ship Gützlaff distributed Bibles off the other. Moreover, in addition to the generous, profit-sharing remuneration given Gützlaff, Jardin and Matheson agreed to pay for the publication of Gützlaff's religious tracts and to purchase medicine imported from Britain for Gützlaff to distribute to the Chinese. Thus, an "opium trading, gun and gospel-carrying vessel" owned by a British company with a missionary as an interpreter began trading up and down the Chinese coast in violation of Chinese law. In the minds of many Chinese the opium trade and Christianity were linked.

Gützlaff worked on a Chinese translation of the Bible, published a Chinese-language magazine, Eastern Western Monthly Magazine, and wrote Chinese-language books on practical subjects. In 1840, Gützlaff (under the anglicized name Charles Gutzlaff) became part of a group of four people (with Walter Henry Medhurst, Elijah Coleman Bridgman, and John Robert Morrison) who cooperated to translate the Bible into Chinese. The translation of the Hebrew part was done mostly by Gützlaff, with the exception that the Pentateuch and the Book of Joshua were done by the group collectively. This translation, completed in 1847, is well-known due to its adoption by the revolutionary peasant leader Hong Xiuquan of the Taipingtianguo movement (who started the Taiping Rebellion) as a reputed doctrine of the Taipings.