WASHINGTON -- Representative Paul D. Ryan, the 42-year-old Republican named on Saturday as Mitt Romney's vice-presidential running mate, is idolized by young conservatives in the House, who see him as a role model and a polished spokesman for their vision of America.
Many Republicans come across as dour budget cutters with contempt for Democrats. Mr. Ryan shares the politics of his conservative colleagues, but appears instead as an optimist who relishes the opportunity to debate policy with Democrats.
Mr. Ryan was first elected to Congress in 1998, at the age of 28, the youngest member of that incoming class. He vaulted to the top ranks of his party and became chairman of the Budget Committee because he knew the ropes, studied the issues and could explain conservative tax-cutting and budget-cutting policies in lucid terms. It has never been enough for him to attack Democrats and their proposals. He has always been eager to propose and defend alternatives, even at significant political risk to himself and his party.
He is hardly a typical committee chairman, a role often played in the House by grizzled old men. An avid hunter, skier and mountaineer, Mr. Ryan listens to heavy metal and indulges in a grueling fitness regimen. At the House gym, he encourages other members to do the same as he coaches them on the intricacies of the federal budget.
Mr. Ryan is fluent -- Democrats would say glib -- in discussing the complex details of health policy.
As Budget Committee chairman, Mr. Ryan has proposed huge changes in entitlement programs like Medicare and Medicaid, changes that would help the federal government predict and control its costs but could shift some costs to beneficiaries and to states.
He would convert the federal share of Medicaid into a block grant, giving each state a lump sum with which to care for low-income people. States would have much more discretion over how to use the money.
To rein in Medicare costs, Mr. Ryan proposes to increase the age of eligibility, cap the growth in costs and have the government give a fixed amount of money to each beneficiary to help buy private insurance.
Democrats said the plan would destroy Medicare. Mr. Ryan did not back off. He tweaked his proposal. He would preserve the traditional fee-for-service Medicare program as an option for beneficiaries, but would force it to compete directly with commercial insurance plans.
In 2010, Mr. Ryan issued a "Roadmap for America's Future" that would have allowed workers under 55 to invest more than one-third of their current Social Security taxes in personal retirement accounts.
The plan would have simplified the tax code, abolishing many tax breaks and eliminating taxes on interest, dividends and capital gains.
Mr. Ryan is a member of the House Ways and Means Committee, which has jurisdiction over taxes, trade and Medicare.
Some Democrats call Mr. Ryan a fiscal phony, saying that by cutting taxes for corporations and the rich, he would perpetuate the deficit. President Obama recently described Mr. Ryan's budget plan as "an attempt to impose a radical vision on our country" and "thinly veiled social Darwinism."
In 2010, Mr. Ryan wrote a book with Representatives Eric Cantor of Virginia, now the House majority leader, and Kevin McCarthy of California, the party whip, setting forth their vision, "Young Guns: A New Generation of Conservative Leaders."
The editors of Human Events named Mr. Ryan "Conservative of the Year" for 2011.
But on Medicare and fiscal policy, he has sometimes worked with Democrats like Senator Ron Wyden of Oregon and Alice M. Rivlin, a former director of the Congressional Budget Office.
Paul Davis Ryan was born in Janesville, Wis., on Jan. 29, 1970, the youngest of four children of Paul and Elizabeth Ryan. He was 16 when his father died of a heart attack. That is one reason, he has said, for his own devotion to physical fitness.
His brother Tobin Ryan said, "The death of my father had an enormous impact on accelerating his development."
Mr. Ryan has been quoted as saying that his family received Social Security survivor benefits after his father's death, and that he used some of the money to help pay for college. So, he says, he appreciates the value of the program.
Mr. Ryan received a B.A. in economics and political science from Miami University in Ohio in 1992 and went to work as an aide to Senator Bob Kasten, Republican of Wisconsin. From 1993 to 1995, he worked at Empower America, a group organized by former Representative Jack F. Kemp of New York and others.
From 1995 to 1997, Mr. Ryan worked as a top aide to Sam Brownback, a Kansas Republican who was then a member of Congress and is now governor.
Before being elected, he worked at Ryan Inc. Central, a construction company founded by his great-grandfather in 1884.
Mr. Ryan and his wife, Janna, have three children, Liza, Charlie and Sam.
This article originally appeared in The New York Times.