By Lindsay Beck

BEIJING, Sept 5 (Reuters) - No one knows better how to ride the political winds within China's Communist Party than Vice-President Zeng Qinghong.

He rose to power as the hatchet man of former leader Jiang Zemin, but as President Hu Jintao consolidates power in his turn, the 68-year-old is emerging from the shadow of his old boss and benefactor to become his own deal-maker among the elite.

"Zeng Qinghong is probably the most mysterious leader at the moment in terms of his position and in terms of his political alignments," said Joseph Cheng, professor of political science at City University of Hong Kong.

Fifth in the Party hierarchy, Zeng, a native of the southern province of Jiangxi, wields more clout than his rank suggests and will be trying to expand that at a key Party congress in October.

Five years ago he began his term on the nine-man Politburo Standing Committee that rules China as Jiang's man, and was said to be waiting in the wings if Hu faltered.

But he has since made his own political name, most notably by working closely with Hu to weather pro-democracy demonstrations in Hong Kong that brought half a million people into the streets, and on Taiwan policy.

Last year, Zeng also went along with Hu's politically charged decision to sack Chen Liangyu as Party boss of Shanghai, the financial hub that was Jiang's political stronghold.

But patronage is a potent force in Chinese politics and Zeng, a rocket scientist-turned-apparatchik, owes his rise to Jiang. Even now, analysts say Zeng remains a key avenue through which Jiang can wield power in retirement.

"He is Jiang Zemin's man, and he will remain as Jiang Zemin's man," said Cheng Li, a China scholar and senior fellow at the Brookings Institution in Washington.

"But he helps Hu Jintao very well. They have some kind of cooperative relationship, but they also compete against each other, not necessarily for power but for policy initiatives."

SON OF THE REVOLUTION

Jiang brought Zeng with him from Shanghai when he was promoted to national leader in Beijing in 1989. There, he helped his boss eliminate opponents and consolidate his grip on the military, whose support was vital to securing Jiang's political longevity.

He went on to lead the influential Organisation Department until 2002, a position that gave him a key role in personnel changes. That background gave Zeng broad experience in organisation and ideology, but his role as Jiang's wing-man also won him his share of enemies.

Analysts say Zeng, his father a revolution-era military commissar and his mother one of the few women who made the Long March, also has built his own political base through the "princelings", the sons and daughters of past leaders.

Zeng has also sought to put his stamp on Party ideology, advocating greater "inner-party democracy" -- the term used to describe increased competition within the ruling hierarchy -- and saying Party members should not be afraid to speak out.

Inner-party democracy was "the key to the improvement of the Party's creativity, governance capability and official integrity", the Xinhua news agency has quoted him as saying.

The ambitious Zeng is said to have his sights on becoming a vice-chairman of the Central Military Commission and wants to be given the chance to cultivate a higher profile abroad.

But despite his expedient alliance with Hu, a simmering rivalry remains, and Hu is unlikely to hand him a platform to build his own power base. There are some who say Zeng will simply retire at the mid-October congress.

For his part, Zeng, the master of manoeuvring, is likely to bide his time, and keep people guessing.

"I think a politically ambitious leader in China certainly understands how to make alliances, and how to build new alliances all the time," said Cheng.

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