Records of the Three Kingdoms
Zhuge Jin, courtesy name Ziyu, was from Yangdu in Langya, Zhuge Liang’s elder brother. He fled the late Han disorders to Jiangdong and was recommended to Sun Quan, who trusted his patience and plain dealing. On missions to Shu he met his brother. The histories say the two did not visit each other in private, so that nobody could accuse them of sharing state secrets.
He spent years on diplomacy with Shu and on the Jing military establishment, and he ended as a senior general. He died of illness in 241, at sixty-eight. Chen Shou praises his bearing and the regard his own age had for him.
His son Zhuge Ke was quick and proud. Sun Quan favored the son late in life; Zhuge Jin worried. After Jin’s death, Ke served as regent for Sun Liang, failed at Hefei, and was killed at a banquet by Sun Jun. That ended the Zhuge house in Wu.
Romance of the Three Kingdoms
The novel sends him back and forth as the envoy who asks Liu Bei to return Jing Province, and has Zhuge Liang or Liu Bei turn him away with speeches. He looks like his brother and yields more easily. That is the role the book gives him.
It also keeps his warnings to Zhuge Ke. Ke’s later monopoly of power and his murder sit in the Wu chapters of the second half, and the father’s worry is planted as a sign of what is coming.
Reference: Wikipedia · Zhuge Jin