King of Qi was the title used by several rebellion leaders during the collapse of Qin dynasty. They were descendants of the old Warring State Qi royal family. The kingdom was roughly the current Shandong province.
From Kingdom of Qi several other Kingdoms derived: Kingdom of Jiaodong, Kingdom of Jibei and Kingdom of Linzi. These three were all among the 18 Kingdoms.
References
Kingdom of Qi Wikipedia(Text) CC BY-SA