The official announcement was made Aug. 11 on the USS Wisconsin in Norfolk, Va., the Washington Post noted. According to CNN, Romney—in introducing Ryan—accidentally called him "the next president" instead of "vice president." Romney later corrected his error, saying, "I'm known to make a mistake every once and a while. I didn't make a mistake with this guy." (CNN.com pointed out that President Obama made the same mistake with Joe Biden in 2008.)

Ryan is 42, the same age as Romney's oldest son, Tagg, Boston.com noted. (Romney is 65.) Ryan was initially elected to Congress at 28.

In accepting the selection, Ryan said, among other things, "Our rights come from nature and God, not government."

He also said, "My dad died when I was young. He was a good and decent man. He said, 'You're either part of the problem or part of the solution.' President Obama has become part of the problem, not the solution."

Ryan chairs the House Budget Committee, where he has played a significant role in drafting and promoting the GOP's long-term budget proposals. Ryan introduced the controversial plan The Path to Prosperity last year; the initiative included controversial changes to Medicare.

Some see the move as Romney's attempt to appeal to a conservative base that has been skeptical of him at times.

Obama for America Campaign Manager Jim Messina released a statement that reads, in part, "In naming Congressman Paul Ryan, Mitt Romney has chosen a leader of the House Republicans who shares his commitment to the flawed theory that new budget-busting tax cuts for the wealthy, while placing greater burdens on the middle class and seniors, will somehow deliver a stronger economy.

"As a member of Congress, Ryan rubber-stamped the reckless Bush economic policies that exploded our deficit and crashed our economy. Now the Romney-Ryan ticket would take us back by repeating the same, catastrophic mistakes."

R. Clarke Cooper, executive director of the LGBT GOP organization Log Cabin Republicans, said in a statement, "Congressman Paul Ryan is a strong choice for vice president, and his addition to the GOP ticket will help Republican candidates up and down the ballot.

"Congressman Ryan's 2007 vote in favor of the Employment Nondiscrimination Act [ENDA] and his consistent willingness to engage with Log Cabin on a range of issues speaks to his record as a fair-minded policymaker. Overall, while Log Cabin Republicans have not completed the endorsement process for the 2012 presidential election, this is a choice that all Republicans can be excited about, and which sends a good message about the kind of campaign Governor Romney wants to run, and the kind of president Governor Romney wants to be."

However, despite Log Cabin's stance, the Human Rights Campaign (HRC) has given Ryan a zero-percent rating. According to HRC, Ryan does not support marriage equality, and he is "not yet a co-sponsor" of measures such as the Respect for Marriage Act, the Uniting American Families Act and the Employment Non-Discrimination Act, among others. When Ryan voted for ENDA in 2007, it did not include gender identity or expression, according to Gay City News.

The publication added that in both the 2009-2010 and the 2007-2008 sessions, Ryan voted against hate-crimes protections. He also did not support repeal of the military's "Don't Ask, Don't Tell" policy in 2010.