Zhou Yongkang, China’s former domestic security chief. (Reuters)

Zhou Yongkang is a former domestic security chief of China, making him the most powerful man to be investigated as part of President Xi Jinping’s anti-corruption campaign.

The probe is rumored to be two years in the making, with party members affiliated with Zhou methodically targeted. If Zhou is expelled from the party and convicted on corruption charges, he would be the highest-ranking party leader to be taken down in decades.

Also read: How the secretive, powerful agency in charge of investigating corrupt Chinese officials works

Timeline of Zhou's career 

December 1942: Born in Xi Qiantou village, Jiangsu province, into an eel fisherman’s family. Zhou has two younger brothers.

1988-1998: Vice head, then head of the state-owned oil conglomerate China National Petroleum Corp., the largest producer of oil and gas in the country.

1998-1999: Served as minister of land and resources

1999-2002: Served as party secretary (top leader) of Sichuan province in southwest China.

2002: Elected to the party's powerful Politburo and elevated to the head of the Ministry of Public Security.

2007: At the 17th party congress in Beijing, Zhou was elevated onto the all-powerful, nine-person Politburo Standing Committee, China’s top ruling body. He was also promoted to the post of secretary of the law and politics committee, having earlier served as the deputy secretary.

During his tenure as security chief and head of the law and politics committee, Chinese government spending on domestic security exceeded even that for its military/international security.

November 2012: Zhou retired. After the retirement, speculation about his downfall and ensuing investigation begin to swirl in the wake of the Bo Xilai scandal. Zhou is thought to be a close ally of Bo, a former rising star in the party who was convicted of corruption.

Dec. 6, 2012: Li Chuncheng, Sichuan's deputy party secretary, became the first senior official to be investigated and targeted in an anti-corruption drive launched by the new leadership. Li was thought to have close ties to Zhou.

Sept. 1, 2013: Jiang Jiemin, head of the State-owned Assets Supervision and Administration Commission, was probed for "serious disciplinary violations." Jiang's and Zhou's career paths overlapped, and Jiang's purge is thought to have diminished Zhou's influence.

Dec. 20, 2013: Li Dongsheng, vice minister of public security, was under investigation over "serious law and discipline violations." He is a close associate of Zhou. Li’s downfall was another heavy blow to Zhou’s power sphere and suggested that the focus of the probe against Zhou had shifted from the oil sector to the public security sector.

December 2013: Zhou was put under house arrest, according to foreign media reports.

July 29, 2014: Zhou was officially placed under investigation, accused of "seriously" violating party discipline.