Beijing: In his first public address as the freshly unveiled President of China, Xi Jinping laconically apologised to the waiting media for being late, introduced the other six members of his standing committee and then proceeded to elucidate the “severe challenges” facing his government – chief among them the graft and corruption engulfing the Communist Party and its credibility.

“To forge iron, you must have a strong hammer,” he said.

Some 20 months later, amid an audaciously wide-ranging anti-corruption campaign, waged simultaneously as he grappled with factional politics to centralise control of the country’s military and national security policies, Mr Xi has his biggest scalp yet.

On Tuesday evening, China announced an investigation into the 72-year-old former domestic security chief Zhou Yongkang, one of the nation’s most feared political identities, and a man who once controlled the country’s police force, state security and lucrative state oil monopoly.

Mr Zhou, as a former member of the Politburo Standing Committee, is the most senior official ever to be investigated for corruption since the founding of the Communist Party – breaking an unwritten rule that standing committee members, past or present, should effectively be immune from investigation in the interests of party stability.

A political rival of Mr Xi, Mr Zhou’s stocks fell sharply after his political ally, disgraced former Chongqing party secretary Bo Xilai, was jailed for life over corruption charges stemming from a cover-up of his wife Gu Kailai’s murder of British national Neil Heywood.

Talk of Mr Zhou’s political demise emerged over two years ago. The detention and arrest of a string of his close associates and political allies provided more concrete clues.

But as time stretched on without a formal announcement, observers wondered whether his lingering patronage among certain party elders would obstruct Mr Xi from getting his man. In the end, the official announcement appears to have come only after his fate has been irrefutably sealed.

“For a highly calculating and risk-averse group of politicians like those around Xi, this shows that they feel they have contained the network they need to and have Zhou snared,” said Kerry Brown, professor of Chinese politics at the University of Sydney.

To get around the country’s internet censors, Chinese media outlets and netizens online have long resorted to creative pseudonyms when referring to Mr Zhou – one of the more popular ones being Kang Shifu, or Master Kang, a brand of instant noodles.

Within minutes of the news of the investigation into Mr Zhou, the ban on using his name appeared to be lifted, allowing discussion of his demise to foster freely on social media.

Unrestrained by reporting restrictions on what previously was a politically sensitive subject, Chinese financial magazine Caijing immediately reported Mr Zhou’s son, Zhou Bin, had been formally arrested for running an illegal business.

Another respected Chinese publication, Caixin, immediately uploaded a five-part series documenting in intricate detail of the rise and fall of the former top politician.

Among the kernels of information were that Mr Zhou, who was born Zhou Yuangen, changed his name in high school because a classmate had the same name. His first wife, Wang Shuhua, died in a car crash while his second wife, Jia Xiaoye, was a broadcaster for state television network CCTV.

But the corruption charges against Mr Zhou will likely centre around the fortune amassed by his son Zhou Bin, and assets held in the name of his mother-in-law, Zhan Minli.

Caixin reported that Zhou Bin was able to obtain control of oilfields and energy assets at low prices, before selling them for a huge profit, “a common practice seen among guan’erdai”, or the privileged offspring of senior officials.

An earlier investigation by The New York Times also showed that Mr Zhou’s family held assets worth at least $US1 billion, according to company and asset records.

Despite the undisputed upheaval of the ongoing corruption purge, observers remain divided over the ultimate motivation of Mr Xi. Himself a ‘princeling’ son of Communist Party revolutionary hero Xi Zhongxun, some see his campaign as an expedient way of ridding himself of political foes.

“The territory once occupied by Mr Zhou will simply be shared by other ‘tigers’ in the Chinese leadership,” said Hu Jia, a dissident rights activist who has been a vocal critic of Mr Zhou. “His fall has nothing to do with anti-corruption; it’s just because he challenged Xi.”

The University of Sydney’s Kerry Brown said the pursuit of Mr Zhou was “payback time” for the disloyalty he showed by backing his protege Bo Xilai.

“He showed that he privileged his own private networks, feeding them with wealth rather than sharing a disciplined vision of the party and its collective aims,” he said.

“This is not a process that has been driven by Xi Jinping as some modern strong man. It is about a leadership who have been forced by the vast challenges now facing China in its journey to middle income status to adopt political efficiencies.

“A China with a falling growth rate can no longer afford the luxury of the sort of vast personal patronage networks of a figure like Zhou.”

with Sanghee Liu