These are the 24 hours François Fillon has waited for. The man from Le Mans today becomes President Nicolas Sarkozy's copilot, the prime minister who will help accelerate his new boss's reform agenda. Fillon, Sarkozy's top political adviser during the hard-fought presidential campaign, becomes his No. 2 and the head of a government to be named tomorrow. The pair are poised to drive through the most comprehensive reforms in modern French history. But they sure make an odd couple.

Sarkozy, 52, and Fillon, 53, are the youngest ticket to lead France since 1980. Yet both have political experience beyond their years. In 1981, Fillon, at 27, became the youngest parliamentarian in France. Sarkozy became the country's youngest mayor two years later, at 28. They've both headed a range of ministries; Fillon, a five-time minister, has headed Education, Social Affairs, Information Technology and the Postal Service. Today, the pair, now the most powerful in France, jog together, often photographed side by side during the campaign, sweat-drenched, in shorts. Fillon races cars and climbs mountains in his spare time. Both have young children; Sarkozy's son Louis is 10; Arnaud, the youngest of Fillon's five children, is 5.

But the similarities end there. Indeed the tensions between them were well enough known that as recently as 2003, Sarkozy reportedly quipped, "They say he's the anti-Sarkozy. It's true. He's neither effective nor popular!" They were rivals for the leadership of the right-wing RPR party in 1999 and in the past disagreed on fundamentals. Sarkozy, apart from a few recent campaign digs at the European Central Bank and the strong euro, has been a fairly faithful European; Fillon, a eurosceptic early on, voted "No" in the 1992 referendum on the Maastricht Treaty that led to the creation of the EU.

But Fillon finally found common ground with the pugnacious future president. After pushing through tough retirement reforms as Social Affairs minister in 2003 despite millions of demonstrators in the streets, he felt he deserved more. When he didn't make the list for Dominique de Villepin's government in 2005, he fought back. "When people look back on Chirac's record, they will remember nothing, except my reforms," he snapped to a Le Monde reporter. Fillon felt betrayed. "In throwing me out, they've made me [Sarkozy's] future campaign director," he declared.

Fillon--generally calm, courteous, prudent, at times even meek--complements Sarkozy, the hyperactive provocateur with the hot-button temper. The Fillons make the Sarkozys, with their pop- star friends and flashy holidays, look like Britain's favorite celeb couple, the Beckhams. Fillon's wife of 27 years, Penelope Fillon, née Clarke, is from Wales. An unpretentious homemaker, she faded into the background in her loose-fitting gray and brown outfit at this morning's brief handover ceremony, as her husband stood, prim and awkward, next to the outgoing de Villepin, much taller and oozing Gallic flair. The Fillons are more comfortable in their chateau, with their horses, in Fillon's native rural Sarthe region than within the Paris beltway; Penelope is said to have made her husband promise to quit politics as soon as he is old enough to retire.

Reputed a fine negotiator, Fillon enjoys the respect of union leaders and has cast himself a reformer on the strength of his performances at Social Affairs, Education, and as Postal Service and Telecommunications Minister in the mid-1990s, when France Telecom's monopoly was ended. (He's known defeat, too. As Education Minister in 2005, he had to leave a measure reforming the high- school-leaving diploma out of his wider system reforms when students took to the streets for months and shut down their schools.) The title of his 2006 book, a reform manifesto, translates as "France Can Handle the Truth."

But one truth Fillon himself can handle will be of great convenience to the new president. Sarkozy is likely to be an exceptionally hands-on head of state, and he will need his prime minister to be no more than a solid sidekick. While their disparate personalities may moderate each other, there will be no question who's boss. That should suit Fillon's personality just fine.