Li Guang, the general, was a native of Chengji in Longxi. His ancestor was Li Xin, a Qin general who had pursued and captured Dan, the Crown Prince of Yan. The family had originally dwelt in Huoqiang before moving to Chengji. Archery had been passed down through generations in the Li household.
In the fourteenth year of Emperor Wen's reign, the Xiongnu mounted a major invasion through Xiaoguan Pass. Li Guang enlisted as a common soldier to fight the nomads, distinguishing himself through exceptional horsemanship and archery, and killing and capturing many enemies. He was appointed a palace guard. His cousin Li Cai also served as a palace guard, both holding the rank of Armed Cavalry Attendant with a stipend of eight hundred dan.
Once, while accompanying the emperor on an excursion, Li Guang had performed brilliantly in skirmishes and wrestled with wild beasts. Emperor Wen remarked, "What a pity you were born in the wrong era! Had you lived in the time of Emperor Gaozu, a title of ten thousand households would have been nothing to you!"
When Emperor Jing first ascended the throne, Li Guang was appointed Commandant of Longxi, then transferred to serve as Cavalry General. During the campaign against Wu and Chu, he served as vanguard cavalry commander under Grand Marshal Yafu, capturing enemy banners at Changyi and earning great distinction. However, because the Prince of Liang had granted him a general's seal, his official rewards were withheld upon his return. He was reassigned as Commandant of Shanggu, where he clashed daily with Xiongnu forces.
The Director of Vassal Affairs, Gongsun Hunxie, tearfully appealed to the emperor: "Li Guang's talents are unmatched beneath heaven. Relying on his abilities, he has engaged the enemy repeatedly—I fear for his life." Consequently, Li Guang was transferred to serve as Commandant of Shangjun. He subsequently held posts as governor of Longxi, Beidi, Yanmen, Dai, and Yunzhong commanderies, earning a reputation for valor in battle.
When the Xiongnu invaded Shangjun in force, the emperor dispatched a high-ranking eunuch to observe Li Guang's military training. The eunuch rode out with several dozen cavalrymen and encountered three Xiongnu scouts. In the ensuing engagement, the scouts loosed their arrows, wounding the eunuch and nearly annihilating his escort. The eunuch fled back to Li Guang, who said, "Those must be expert archers—men who shoot down eagles from the sky."
Li Guang then took a hundred riders to pursue the three men. They had lost their horses and were on foot, having walked several dozen li. Li Guang ordered his cavalry to spread out on both flanks while he rode forward alone. He killed two of the three and captured the third—an archer who could bring down eagles. As they bound the prisoner, they spotted several thousand Xiongnu cavalry in the distance. The nomads, mistaking Li Guang's force for a decoy party, panicked and raced up a hillside to take formation.
Li Guang's hundred men were terrified and urged flight. He addressed them: "We are scores of li from the main army. If we flee now, the Xiongnu will cut us down in moments. But if we hold our ground, they will assume we are bait for a larger force and dare not attack." He then commanded: "Forward!"
When they had closed to within two li of the Xiongnu lines, he ordered: "Dismount and loosen your saddle girths!"
His riders protested: "The enemy is many and near—what if they attack?"
Li Guang replied: "They expect us to run, so we loosen our saddles to show we intend to stay. This will dispel their suspicion."