Yesterday, the Spanish Socialist leader threw thousands of delegates at the party's congress in Madrid into turmoil with the shock announcement that he would not stand again as candidate for Secretary-General. He said that it was time for a new generation to rule Spain's principal opposition party.
He is known to be tired and politically aged beyond his 55 years. But he is also renowned as a consummate political operator who never ceases to spring surprises, and it may be that this is another political ploy.
Mr Gonzalez had been party leader since 1974 when he was elected unexpectedly at a clandestine congress held near Paris during the Franco dictatorship. No plausible candidate emerges immediately as a possible successor, but among those mentioned are Joaquin Almunia, a spokesman for Mr Gonzalez, Josep Borrell, a pushy former socialist minister; and Javier Solana, now Secretary-General of Nato.
It was no secret before last year's elections, when the Socialists were defeated after nearly 14 years in power, with Mr Gonzalez as Prime Minister, that the socialist leader was stale, dispirited, and wanted to quit.
But he threw himself wholeheartedly into an enthusiastic campaign, pulling out all the stops, and is credited personally with having held his party to within a whisker of winning the election.
The Popular Party, led by the Prime Minister, Jose Maria Aznar, achieved only a relative majority, and today depend on votes from the Catalan nationalists to rule.
The Socialists, accused of corruption and undercover death squads against Eta suspects, had become discredited and bereft of ideas. Their unexpectedly good result is directly attributable to the personal prestige and popularity of Mr Gonzalez, who, since he burst upon the Spanish political scene more than 20 years ago, has not ceased to dominate it. This is partly because of his undoubted charisma, and partly, critics say, because of his supreme talent for destroying potential rivals within his own party before they became a threat to his leadership.
This is not the first time he has threatened to leave his comrades in the lurch.
At the party's congress in 1979, when the Socialists for the first time began to realise they might win power in Spain's new democracy, he suddenly plunged into a hectic debate about whether or not the party should renounce its commitment to Marxism, saying that he would quit unless they abandoned what he considered to be outmoded revolutionary rhetoric.
Then, as now, the comrades, hitherto all full of intrigue about internal politics, were left speechless and rudderless.