Late Goryeo Neo-Confucian scholar and official, known as Master Yeokdong for his axe-in-hand remonstrance to King Chungseon

| Life | 1262 ~ 1342 |
| Era | 고려 후기 |
| Clan | 단양 우씨 |
U Tak (1262-1342) was a late Goryeo civil official and scholar of the Danyang clan, with courtesy names Cheonjang and Takbo and pen names Baegun and Danam. He later came to be called Master Yeokdong for his command of the Book of Changes, and his posthumous title is given as Munhui. A seventh-generation descendant of the founder U Hyeon, he was the son of U Cheon-gyu. Sources give his birth year as 1262 or 1263.
He became a provincial licentiate in 1278 and, passing the examination, was made Yeonghae sarok, where he is said to have abolished a shrine to a false spirit. In 1308, the year King Chungseon took the throne, he was a censorate corrector (gamchal gyujeong). When in November the king consorted with a concubine of his late father, U Tak entered the palace in white clothes carrying an axe and a straw mat to remonstrate. The vice-minister who remonstrated with him, O Yeon-gyeong, was banished and died young, while U Tak withdrew to the countryside to study. Later called back by King Chungsuk and his ministers in recognition of his loyalty, he retired as Seonggyun jwaeju (Chancellor of the Seonggyungwan).
After leaving office he lived in seclusion in Yean (around present-day Andong) and devoted himself to teaching. He studied Cheng Yi's Commentary on the Changes, which reached Korea through Yuan China; since nobody could understand it at first, it is said he shut himself in for about a month until he mastered it and then taught his students. Well versed in the classics and history and especially in Yijing studies, he is regarded as a key figure in the early transmission of Neo-Confucianism to Korea. The sijo "Tanrōga," lamenting old age, is also attributed to him.
In 1308, as a censorate corrector, U Tak is said to have entered the palace in white clothes with an axe and a straw mat on his back to correct the conduct of King Chungseon. The episode is often cited as a model of such an axe memorial, and O Yeon-gyeong, who remonstrated with him, was banished.
After retiring he taught Cheng Yi's Commentary on the Changes to his students in Yean. He is always mentioned in accounts of the early adoption of Neo-Confucianism in Korea, and with U Hyeon-bo of the same clan he represents the Danyang U clan in late Goryeo.
Sainam, one of the Eight Scenic Spots of Danyang, is said to be named for the post of sain he held when he rested there. Yeokdong Seowon honoring him was founded in Andong in 1570 on the proposal of Yi Hwang, received a royal charter in 1684, was torn down during the academy abolition, and was restored at its present site in 1969.
The location of his tomb was not confirmed in the sources used here. He taught in Yean near Andong, where Yeokdong Seowon honors him; the Yeokdong relic monument is Gyeongsangbuk-do Tangible Cultural Heritage No. 30.
His father was U Cheon-gyu, and he was a grandson of the mid-founder U Jung-dae; U Cheon-seok, the third son of U Jung-dae, was his uncle, and U Cheon-seok's great-grandsons were U Hyeon-bo and U In-yeol.