(연남생, 淵男生) (634-679) was the eldest son of the Goguryeo Dae Mangniji
(대막리지, 大莫離支) Yeon Gaesomun
(603?-665). In 665, Yeon Namsaeng succeeded his father and became the 2nd Dae Magniji of Goguryeo
Yeon Namsaeng was the eldest son of Goguryeo's Grand Prime Minister Yeon Gaesomun
. At the age of nine, his father began to bequeath him official positions. He first became Seonin
(선인, 先人) and subsequently held the titles of jungli sohyeong
(중리소형, 中裏小兄), jungli daehyeong
(중리대형, 中裏大兄), and jungli uidu daehyeong
(중리위두소형, 中裏位頭大兄) (obscure Goguryeo titles whose exact nature is unknown). Eventually he rose to become Mangniji
(막리지, 莫離支) and then Dae Mangniji
(active head of state) sometime before his father's death.
Yeon Namsaeng was said to have become Dae Magniji sometime before the death of Yeon Gaesomun, who is said to have stepped down from the position and took the honorary position of Tae Dae Magniji
After the death of his father, Yeon Namsaeng prepared for war with the Tang, and set out on an inspection of the border fortresses in Yodong, and other fortresses throughout the kingdom. He left his brothers, Yeon Namgeon and Yeon Namsan, in charge of Pyeongyang before he left. Namgeon and Namsan took advantage of their brother's absence and took control of Pyeongyang and the Royal Courts. They falsely accused Namsaeng of being a traitor, and forced the King Bojang to order Namsaeng's arrest. With nowhere else to go, Namsaeng fled to Tang China at the urge of his son, who had escaped death at the hands of his uncles. Namsaeng fled to the Tang, and received a high position in the Tang military.
Fall of Goguryeo and death
From there he led a Tang-sponsored military campaign against Goguryeo with hopes of regaining power. He led the Tang army to victory in 668, and ultimately destroyed Goguryeo. He died in the domains of the Tang-established Protectorate General to Pacify the East
, or Andong Duhufu (安東都護府), the Chinese administration established in Pyongyang
following the fall of Goguryeo in 668 and meant to administer the former Goguryeo domains. Namsaeng was buried on Mt. Mang in Luoyang
, Tang’s eastern capital.
Namsaeng's tomb stele, along with that of his brother Namgeon, has been discovered. Namsaeng's biography (Quan Nan Sheng 泉男生傳) appears in the Xin Tangshu (New History of Tang), book 110. The Chinese rendering of Namsaeng’s family name is Cheon (泉, Chinese Quan) rather than Yeon (淵), because Yeon (Chinese, Yuan) was the given name of Emperor Gaozu of Tang (Li Yuan 李淵), founder and first emperor of Tang, and taboo to apply to another by Chinese tradition.