Ahn Jung-geun or An Jung-geun (September 2, 1879 - March 26, 1910) (Baptismal name: Thomas) was a Korean independence activist, nationalist, and pan-Asianist.
He assassinated the first Prime Minister of Japan, Itō Hirobumi, following the signing of the Eulsa Treaty, with Korea on the verge of annexation by Japan.
An was born in Haeju, Hwanghae Do, to a family of the Sunheung An lineage. He worked first in education, later joining the armed resistance against the Japanese colonial rulers. While fleeing the fighting he took refuge with a priest of the Roman Catholic Church named Wilhelm (Korean name, Hong Sok-ku) and hid in his church for several months. The priest encouraged An to read the Bible and after a series of discussions with Wilhelm, An converted to Catholicism in January 1897. He maintained his belief in Catholicism until his death, even asking his that his son become a priest in his last letter to his wife.
An Jung-geun assassinated Ito Hirobumi on the railway platform in Harbin, Manchuria in 1909. After firing upon Hirobumi, he yelled for Korean independence and waved the Korean flag. Afterwards he was arrested by Russian guards who held him for two days before turning him over to Japanese colonial authorities. When he heard of the News that Ito had died, he made the sign of the cross in gratitude. An was quoted as saying "I have ventured to commit a serious crime, offering my life for my country. This is the behavior of a noble-minded patriot." Despite the orders from the Bishop of Korea not to administer the Sacraments to An, Fr. Wilhelm disobeyed and went to An to give An the Last Sacraments. An insisted that the captors call him by his baptismal name, Thomas.
His Japanese captors showed sympathy to An. An recorded in his autobiography that the public prosecutor, Mizobuchi Takao, exclaimed "From what you have told me, it is clear that you are a righteous man of East Asia. I can't believe a sentence of death will be imposed on a righteous man. There's nothing to worry about." He was also given New Year's delicacies and his calligraphy was highly admired and requested. An was sentenced to death by the Japanese colonial court. An was angered at the sentence, though he expected it. He had hoped to be viewed as a prisoner of war instead of an assassin. Judge Hirashi, who presided over An's trial, had promised An that a stay of execution for at least a few months would be granted, but Tokyo ordered prompt action. An did not appeal the verdict, though he did ask for the warden's help to finish his essay, "On Peace in East Asia" and for a set of white silk Korean clothes to die in. The warden was able to grant the second request and resigned shortly afterwards. An requested to be executed as a prisoner of war, by firing squad. But instead as a common criminal it was ordered that he should be hanged. The execution took place in Port Arthur, then also known as Ryojun on March 26, 1910. Itō's death resulted in the acceleration of the final stage of the colonization process.
According to Donald Keene, author of "Emperor of Japan: Meiji and His World, 1852-1912", An Jung-geun was an admirer of Emperor Meiji of Japan. One of the 15 'charges' An leveled against Ito was that he had deceived the Emperor of Japan, whom An felt desired peace in East Asia and Korean independence. An requested that Meiji be informed of his reasons for his assassination of Ito in the hopes that if Meiji understood his reasons, the emperor would realize how mistaken Ito's policies were and would rejoice. An also felt sure that most Japanese felt similar hatred for Ito, an opinion he formed from talking with Japanese prisoners in Korea. While An was staying in the prison and on the trial, many Japanese prison guards, lawyers and even prosecutors were inspired by An's great spirit, righteousness, and humanity.
For his actions as a resistance fighter, he was awarded South Korea's Order of Merit for National Foundation in 1962.
An strongly believed in a union of the three great countries in East Asia, China, Korea, and Japan in order to counter and fight off the "White Peril", being the European countries engaged in colonialism, restoring peace to East Asia. He followed the progress of Japan during the Russo-Japanese War and claimed that he and his compatriots were delighted at hearing of the defeat of one of the agents of the White Peril, but was disappointed that the war ended before Russia was totally subjugated.
An felt that with the death of Itō, Japan and Korea could become friends because of the many traditions that they shared. He hoped that this friendship, along with China, would become a model for the world to follow. His thoughts on Pan-Asianism were stated in his essay, "On Peace in East Asia" that he worked on and left unfinished before his execution.
 Calligraphy works
"一日不讀書口中生荊棘" means "Unless reading everyday, thorns grow in the mouth."
An is highly renowned for calligraphy works. An's calligraphy works have been respected not only for his artistic skills but also honourable spirit, which is reflected on his works. While he was staying in the prison, many prison guards such as Toshichi Chiba who respected him, requested An for calligraphy works. He left many calligraphy works which were written in the jail of Yeosun (Lushun) although he hadn't studied calligraphy formally. Some of the works were designated to Treasures No. 569 of Korea republic in 1972. His famous work is "一日不讀書口中生荊棘"(Korean pronunciation: il il bu dok seo gu jung saeng hyeong geuk, Meaning: Unless reading everyday, thorns grow in the mouth.) This has been widely quoted by people who wanted to give emphasis to reading and studying.
 In popular culture
He is commemorated in the martial art Taekwondo with the Joon Gun pattern being dedicated to him.
Novelist Bok Geo-il's 1987 novel Looking for an Epitaph (碑銘 (비명)을 찾아서) is an alternate history story, which is set in the 1980s of Korea that remained a permanent colony of Japan, as a cascade effect of An's failure to assassinate Ito. The Korean movie 2009 Lost Memories is very loosely based on the novel but tells a completely different story. In the Korean film, An Jung-geun is spotted and killed by Japanese soldiers before he is able to shoot Ito Hirobumi. The subsequent butterfly effect makes Japan join the allied side during World War II and become a permanent member of the UN Security Council, enduring the Japanese colonial rule of Korea till the beginning of the 21st century.