WASHINGTON -- Paul Ryan has made a startling rise in the past four years from a relatively obscure congressman representing southern Wisconsin to the darling of conservative thinkers and now Mitt Romney’s choice as the Republican candidate for vice president.

He’s done it with hustle, affability and a sweeping manifesto that Republicans in Congress have embraced as their vision for the future and that includes a hugely controversial transformation of Medicare, the country’s health insurance program for people 65 and older.

Ryan, a fit 42-year-old policy wonk with a relaxed and noncombative demeanor, has become a superstar, a lightning rod and the new identity of the GOP.

The House of Representatives Republican caucus voted nearly unanimously for Ryan’s budget plan in March, and House Speaker John Boehner, R-Ohio, hailed him Saturday as a “reformer and proven leader who will be a great partner to Gov. Romney.” Republican colleagues called him a serious mind, a person who immerses himself in the details and offers a solution instead of just criticizing the president’s policies.

Ryan is also known for a willingness rare among ambitious politicians to take risks, such as pushing to transform the popular but financially challenged Medicare program by cutting spending on future retirees and offering them a subsidy to buy private insurance. He isn’t known for compromising with Democrats to find common ground that could make it through the partisan divide in Congress and become law.

Florida Democratic Rep. Debbie Wasserman Schultz described Ryan as a true believer and an extremist who by force of personality and with the help of tea party-inspired freshmen took control of the House Republican caucus from its leaders. Wasserman Schultz serves on the House Budget Committee, which Ryan chairs, and also leads the Democratic National Committee.

“I have watched him craft one of the most extreme visions for our economy I have ever seen,” Wasserman Schultz said Saturday in an interview. “Paul Ryan is a pleasant enough person. I get along with him well; he’s not acerbic. But his policies are really backward.”

Ryan’s path to vice-presidential choice started in Janesville, Wis., where he was born and still lives with his wife, Janna, and their three children. It’s a riverfront city of 63,000 people that’s just over 75 miles from Milwaukee and a little further than that from Chicago. The Irish Catholic Ryan family has been prominent in the town for five generations, starting a major road construction firm.

Ryan’s life changed as a 16-year-old when he found his father dead of a heart attack. He’s called it a defining moment in which he decided he needed to step up in life.

Ryan was class president and prom king in high school, with his classmates naming him “biggest brown-noser” his senior year. Ryan went to college at Miami University in Ohio, where he met William Hart, an outspoken libertarian professor of economics.

Hart recalled in an interview Saturday that Ryan was already a conservative in college, and one who stood out for his intellectual curiosity. The two became fast friends, and met to discuss political philosophy.

Hart said he spoke to Ryan about philosopher Ayn Rand. Ryan later credited Rand as an influence for him going into public service, describing it as “individualism vs. collectivism.” Ryan told The Weekly Standard in 2003 that he gave Rand’s books as gifts and tried to make his interns read them. He’s since distanced himself from Rand’s teachings, saying in particular that he never believed in Rand’s atheism.