Among other things, supporters say Ryan, author of the GOP's House budget plan, brings youth, conservative bone fides and roots in a swing state to the campaign.
A native and still resident of Janesville, Ryan was elected to Congress at age 28. Now 42, he's chairman of the House Budget Committee and a senior member of the Ways and Means Committee.
Ryan came to the Congress with extensive political experience gained from his work with some of the party's heavy-hitters in the U.S. Senate. He was an aide to then-Sen. Robert Kasten of Wisconsin in the early 1990s, and later served as legislative director for then-Sen. Sam Brownback, now the governor of Kansas.
In 1996, he was a speechwriter for Jack Kemp's vice presidential campaign.
Once in Congress, Ryan helped organize "Young Guns," a program that recruits candidates to run in districts held by Democrats.
The conservative Ryan is seen as one of the Republican Party's lightning rods and his youth could appeal to a demographic considered to lean toward President Obama, and Wisconsin is considered a battleground state.
Ryan does have political baggage. Critics note he's never run a statewide race. He has no foreign policy experience. The heaviest suitcase, however, may be that the budget plan he formulated would, as Democrats claim, "end Medicare as we know it."
Ryan's budget proposes privatizing Medicare for people less than 55 years of age, and funding Medicaid and the Supplemental Nutrition Assistance Program through block grants to the states, among other things. It would shore up Medicare by giving seniors a cash grant to apply to the healthcare coverage of their choice, be it from private insurance companies or a government-run program.
During his acceptance speech at the Republican National Convention in August in Tampa, Fla., Ryan said a Romney-Ryan White House "will not duck the tough issues; we will lead. We will not spend four years blaming others; we will take responsibility. We will not try to replace our founding principles; we will reapply our founding principles."
Ryan married Janna Little, a tax attorney, in 2000. They have three children, Liza, Charles and Sam.