King Xi of Yan (燕王喜) (? - ?) (ruled 255 BC – 222 BC) was the last sovereign of the state of Yan in the last days Warring States period of Chinese history. He was the son of King Xiao of Yan (燕孝王). He was born as Ji Xi (姬喜), the same name of King Lie of Zhou (周烈王) and Count Yi of Cao (曹夷伯).
In the 28th year of his reign, the State of Qin began its conquest of Yan. Seeing the deep situation in which Yan was in, Crown Prince Dan of Yan, King Xi's son, sent an assassin Jing Ke to kill the Qin emperor but this failure only helped to fuel the rage & determination of Ying Zheng, and he increased the number of troops to conquer the state of Yan and order Wang Zhan to destroy Yan. The bulk of the Yan army at the frozen Yishui River, Ji (薊) fell the following year and the ruler, King Xi, fled to the Liaodong Commanteray. To appease the King of Qin, King Xi had his own son executed by decapitation.
In 222 BC Liaodong fell as well, and Yan was totally conquered by Qin under the general (王賁), the son of Wang Jian. King Xi of Yan was captured alive, and his fate is not known. Yan was the third last state to fall, and with its destruction the fates of the remaining two kingdoms were sealed.
All except King Xi were featured in the Chinese period epic The Emperor and the Assassin.