King Heondeok of Silla (Hanja: 憲德王; died 826; Reigned: 809–826) whose born as Kim Eon-seung (김언승/金彦昇) was the 41st ruler of Silla Dynasty. He was the younger brother of King Soseong, son of Crown Prince Hyechung Kim In-gyeom (혜충태자 김인겸/惠忠太子 金仁謙) and served as regent during the reign of Aejang.
In 790, Heondeok traveled to Tang China where he distinguished himself and received a high position. He returned to Silla, becoming regent after the death of his brother. In 809, he slew the now-adult Aejang and took the throne for himself.
In 810, Heondeok repaired the country's irrigation facilities. He also sent his son Kim Heon-jang to Tang with gold and silver Buddhist images to pray for the emperor's eternal peace. Heondeok's later reign saw the rebellion of Kim Heon-chang in 822, and that of Kim's son (Kim Beom-mun) in the following year. Both were suppressed. In 824, troubled by threats from the north, the king ordered a 300-ri-long wall built near the Taedong River, which was then the country's northern border.
The Royal Tomb of King Heondeok in Dongcheon-dong 80-beonji, Gyeongju City, Northern Gyeongsang Province is the typical royal tomb of the unified Silla, equipped with surrounding stone statues carved as literary men, soldiers, lions and the 12 oriental zodiac images like those in the Gwaereung Tomb (Royal Tomb of King Wonseong) or the royal tomb of King Heungdeok, but some of the features of the tombs were missing due to a flood caused by the nearby Bukcheon River. Only five of the 12 zodiac images remain today.