Accession to the throne

Duke Xiao's father was Duke Huan of Qi, who was the first of the Five Hegemons, the most powerful rulers of the Spring and Autumn period. Duke Huan had at least three main wives who bore no sons, six favoured concubines, and more than ten sons. Duke Xiao was then known as Crown Prince Zhao, and his mother was Zheng Ji, a princess of the State of Zheng. Five other sons of Duke Huan also contended for the throne: Prince Wukui, Prince Pan (later Duke Zhao), Prince Shangren (later Duke Yi), Prince Yuan (later Duke Hui), and Prince Yong.

When Duke Huan died in the tenth month of 643 BC, the six princes fought each other for the throne. After two months of fighting Wukui prevailed and ascended the throne in the twelfth month. Crown Prince Zhao fled to the State of Song. During the unrest Duke Huan's corpse lay unattended for 67 days, and it was so badly decomposed that worms crawled out of his room.

Wukui sat on the throne for only three months before being killed. In the third month of 642 BC, Prince Zhao returned with the army of Duke Xiang of Song. The people of Qi killed Wukui and wanted to install Prince Zhao on the throne, but the supporters of the other four princes attacked and drove Prince Zhao back to the State of Song. Two months later, the Song army returned and defeated the forces of the four princes, and Prince Zhao finally ascended the throne, to be known as Duke Xiao of Qi.

Reign

In 637 BC Duke Xiao held a conference of state leaders in order to reconfirm the hegemony of the state of Qi over the other states. However, Duke Xiang of Song refused to acknowledge Qi's hegemony as he aspired to be the hegemon himself. Duke Xiao attacked Song to punish Duke Xiang's disobedience, even though it was Duke Xiang of Song who helped him ascend the throne six years before.

Duke Xiao reigned for ten years. After he died in 633 BC, Prince Kaifang (開方) of Wey, who had been a trusted official of Duke Huan, killed Duke Xiao's son and helped Prince Pan usurp the throne. Prince Pan is posthumously known as Duke Zhao of Qi.

Ancestry

成語「有恃無恐」的典故

魯僖公二十六年（前634年）夏，魯國大饑，齊孝公趁機攻魯。魯大夫展喜先向展禽（柳下惠）請教應對之策後日夜兼程，在齊魯邊界上遭遇孝公，以牛羊、酒食犒勞齊國軍隊。

以下展喜說的話就是展禽教的。

展喜說：「敝國國君聽說貴國君親自舉起了尊貴的雙腳，將親自造訪敝國，所以使下臣以牛羊、酒食犒勞貴國各位執政。」齊孝公問：「魯國人聽說我要來，會感到害怕嗎？」展喜說：「小人(無知無識的平民)可能感到害怕，但君子(執政及知識份子)則不感到害怕。」孝公問：「屋內什麼都沒有，像是中空而懸掛著的磬(一種敲擊樂器)，田野間連青草都沒了，你們是憑著什麼而不怕我呢？」展喜說：「憑著先王的遺命啊！以前我國先祖周公跟貴國先祖太公輔助王室，為成王的左右手，成王獎勵周公、太公的功勞，封其後代於齊、魯，使其相鄰而結盟，盟辭說：『世世的子孫都不得彼此危害。』盟辭藏在盟府，由太公管理著。貴國先君桓公因此糾合諸侯，而攻擊對王室不恭者；彌補各國的缺失而匡救各國的災難，便是昭顯太公所管理的盟約之神聖。所以齊侯您一即位，諸侯都引領期盼著，相互傳言著：『齊侯必能繼承、發揚桓公的功業！』所以敝國不敢發展武力、設置邊防，認為：『難道齊侯繼位才九年，就把先王的遺命、太公的舊職都給廢棄不管了？這樣要如何面對先君桓公？您一定不至於如此的。』所以敝國才能不感到害怕。」齊孝公於是退兵。