WASHINGTON -- Just who is Newt Gingrich anyway?

Is he the big thinking rhetorical bomb-thrower who led Republicans to power in the House of Representatives in 1994 for the first time in four decades, only to have his troops rebel against him four years later?

Is he the undisciplined, self-absorbed House speaker who admitted that a 1995 shutdown of the federal government was prompted in part by what he perceived as a cold shoulder and shabby treatment by President Bill Clinton during a long Air Force One flight?

Is Gingrich the do-as-I-say-not-as-I-do leader who pushed for Clinton’s impeachment in 1998 stemming from his affair with White House intern Monica Lewinsky even while having an affair of his own with a congressional aide?

Or is he the professorial, adult in the room, elder statesman seen on TV during this year’s Republican presidential debates — a forum that’s helped catapult him from the bottom tier to the top rank of GOP White House hopefuls. Gingrich now leads in national and early-primary-state polls and is increasingly viewed as the top conservative alternative to the other front-runner, former Massachusetts Gov. Mitt Romney.

"Anybody who looks at me as a 68-year-old grandfather and says, ’All right, has he grown wiser, has he learned from his experiences, is he somebody that I would trust to lead the American people?’" Gingrich said recently on Fox News’ "Fox & Friends." "They’ve got to come to their own judgment about that."

As he seeks the Republican presidential nomination, even Gingrich concedes that choice could be a difficult call for voters, as his life — both political and personal — has been a rollercoaster ride of soaring highs and messy lows.

"My tenure as Speaker has been marked by both unprecedented accomplishment and unprecedented conflict," Gingrich penned in the liner notes to Lessons Learned the Hard Way, his 1998 mea culpa book. "I have learned some difficult lessons that will shape my outlook forever."

Gingrich has been hailed for being a brilliant political strategist who authored the "Contract with America," a 10-point conservative legislative agenda that served as the cornerstone for the GOP takeover of the House in 1994.

As speaker, Gingrich played a significant role, along with the Clinton White House, in revamping the nation’s welfare system and balancing the federal budget, his supporters say.

"He focused on those things," said former Rep. Robert Walker, R-Pa., a Gingrich friend and campaign surrogate. "Newt does spin out ideas like every minute because he thinks that way. Sometimes it comes off that he’s not focused, but he is, and has accomplishments to prove it."

But his tenure in Congress was also controversial: He earned a reputation as a hyper-partisan, polarizing figure from his sharp attacks on Speaker Jim Wright, D-Texas, which produced an ethics investigation into Wright and led to his resignation in 1989.

Gingrich later went through a rigorous ethics probe into his own activities that in January 1997 resulted in him becoming the first speaker to be reprimanded by the House. He was forced to pay a record $300,000 fine for violating tax law and lying about it to the House Ethics Committee.

Gingrich’s ethics woes, concerns that he was a political albatross that dragged House Republicans to a disappointing performance in the 1998 elections, and fears that he was going soft on the Clinton White House were too much for some House GOP lawmakers.