Viktor Yanukovych has been accused by President Viktor Yushchenko of trying to seize power - an accusation which has led to the president calling a fresh election for May.
The standoff comes after Mr Yanukovych made a dramatic comeback in Ukrainian politics last year, which followed the humiliation of seeing his 2004 official victory in the presidential election snatched away from him.
The 2004 result was cancelled on grounds of electoral fraud and victory went to the "Orange Revolution" led by Viktor Yushchenko.
In the presidential race Mr Yanukovych was seen as outgoing President Leonid Kuchma's man - identified with an unpopular administration accused of corruption and economic mismanagement.
Grassroots support
He also had the open support of Russian President Vladimir Putin.
But in the parliamentary election campaign last year, he skilfully made use of the tactics that helped the Orange Revolution to triumph - employing American consultants, staging rock concerts and prominently displaying his blue-and-white flags and banners on tour.
He shored up his grassroots support in the mainly Russian-speaking industrial southeast of Ukraine, where many voters are suspicious of the pro-Western, liberal Orange Revolution agenda.
His Party of the Regions accuses Mr Yushchenko and the Orange Revolution team of plunging Ukraine into an economic crisis.
His party wants to restore close ties with Russia - ties that were strained by the pro-Western liberal policies pursued by Mr Yushchenko and his team.
Mr Yanukovych also wants more powers devolved to the regions. His strongest support is in Donetsk, Kharkiv, Lugansk and Crimea.
Meteoric rise
Born into the family of a metalworker and a nurse in the eastern town of Yenakiyevo in July 1950, Mr Yanukovych had a troubled childhood.
He was twice jailed for violent crimes in his youth but his official biography states that his convictions were eventually quashed.
"I came from a very poor family and my main dream in life was to break out of this poverty," he once told journalists.
Beginning his career as a transport executive in the Soviet Union's key coal-mining industry in eastern Ukraine, he became a Doctor of Economics - the equivalent of a PhD - in 2000.
He became governor of the Donetsk region, home to more than three million people and the economic powerhouse of Ukraine, less than a year after entering the local administration.
Some see him as the figurehead of Donetsk's political and business groups and associate him with local oligarch Rinat Akhmetov.
Supporters say Donetsk secured unprecedented levels of investment during his governorship.
Language problem
Former President Leonid Kuchma appointed him prime minister in November 2002.
Although he learned Ukrainian after taking office, Mr Yanukovych often finds it difficult to express himself in literary Ukrainian and switches to Russian when dealing with difficult subjects.
Mr Yanukovych's opponents have often made fun of his appearance - he is almost two metres tall (6ft 6ins) and is reported to weigh at least 110kg (240lb).
He has often played up his physical prowess, stressing his skills as a parachutist and a pilot.
Given this, he was widely ridiculed after the 2004 "egg incident" in Ivano-Frankivsk, when an opposition activist threw an egg at him in public.
Mr Yanukovych collapsed to the ground, groaning and clutching his chest.
Initially hospitalised in intensive care, he recovered within hours and went on television to say he felt sorry for the "wayward" youngster who had thrown the egg.
^ Back to top | BBC Sport Home | BBC Homepage | Contact us | Help | ©
~RS~q~RS~~RS~z~RS~03~RS~)