Without question, it's the first thing people notice about Energy Secretary Ernest Moniz. Parted on the left, cut only by his wife, Naomi, the long gray mop resembles Gene Wilder's in "Young Frankenstein."

"I thought, 'Here's a wacky scientist.' " That was the first impression of Elgie Holstein, former Energy Department chief of staff in the Clinton administration, who worked with Moniz at the agency. "And then over time it clearly became something of a trademark. It's perhaps a little neater now and grayer now."

Like Wilder's titular character, Moniz is prone to experimentation and risk.

He's most comfortable in the laboratory, having overseen the national labs as President Bill Clinton's energy undersecretary. He's also stumped for reopening the department's loan guarantee program, which he says will spark innovation in nuclear power and carbon capture and sequestration technology -- both he says are necessary to address climate change.

Former Sen. Pete Domenici said Moniz has revived the department since it awarded failed solar panel-maker Solyndra $535 million in federal backing through the stimulus loan guarantee program -- a debacle that led to an unceremonious end for predecessor Steven Chu.

"He has the makings to be one of the best secretaries of Energy we've had," said the six-term New Mexico Republican, who worked with Moniz as the Senate Energy and Natural Resources Committee chairman and on an independent nuclear waste panel. Domenici is now a senior fellow at the Bipartisan Policy Center.

Moniz, 69, is brainy, for sure — hardly surprising for someone who earned a Ph.D. in theoretical physics at Stanford (he also holds a bachelors in physics from Boston College) and who spent 22 years on the faculty at MIT, the last four as head of the physics department.

Those who know the Fall River, Mass., native say his humorous demeanor (he's quick with a Monty Python reference), personable nature and political experience combined with his scientific background have won him fans across the political spectrum.

"His 97-0 confirmation vote [last year] was a reflection that nobody would ever think of Ernie Moniz as an ideological guy," said Holstein, who is now with the Environmental Defense Fund.

That's key for Moniz, who faces challenges on several fronts.

He's had to reassure Appalachia that the Obama administration isn't trying to kill off coal despite rules curbing greenhouse gas emissions; he's fended off criticism from environmentalists for embracing natural gas and hydraulic fracturing; and he's trying to build support for President Obama's climate agenda in a politically fractured environment.

Most pressing is whether to expedite approvals of natural gas exports. Pointing to the crisis in Ukraine, where Russian President Vladimir Putin used his stranglehold over natural gas supplies as a political weapon, supporters say U.S. exports could weaken Russia's hand in Central and Eastern Europe.

Republicans and some Democrats say the Energy Department is moving too slowly on applications for exports to nations lacking a free-trade agreement with the U.S. Moniz says he's moving through the remaining 24 applications "expeditiously."

House Energy and Commerce Committee Chairman Fred Upton, R-Mich., said a report the committee released on the benefits of natural gas exports was "a friendly shot across the bow" to speed up decisions.

Domenici said the department's recent approval of a seventh export terminal shows Moniz is aware of the stakes.

"I would think it probably got done a little quicker than it might have if he wasn't there. He understands what the Russians are up to," Domenici said.

Moniz understands more than the Russians. Much, much more.

He presided over deeply researched studies covering a host of energy technologies as the executive director of the MIT Energy Initiative, or MITEI, which he started and ran from 2006 until joining the Obama administration.

Those studies allowed Moniz to do what he does best — dig into topics, develop analytical frameworks and reach out to people with a variety of opinions to arrive at common ground.

That's the kind of discipline he brings to Energy, said Melanie Kenderdine, Moniz's energy counselor.

"[Moniz] is an absolute joy to work with if you like to be challenged and work very hard," Kenderdine said. "I often feel like he is staffing us, as opposed to us staffing him."

Bob Armstrong, who now runs MITEI after serving as Moniz's deputy, agreed, saying the Energy secretary never asks anyone to do something he wouldn't.

"He has a clear idea of where he wants to go and getting people to buy in and adjust a vision," Armstrong said.

Where Moniz is going next is uncharted territory for the agency.

He created a new role for Kenderdine to execute his brainchild, the Quadrennial Energy Review, which he recommended as co-chairman of an outside panel to Obama. The project, due Jan. 31, is assessing the nation's entire energy infrastructure.

Policymakers often say the U.S. lacks a national energy policy. But experts agree the review, the first of its kind, could serve as a policy framework for years to come.

Who better to execute such a grandiose plan than a wacky scientist?

"Ernie has always been very motivated to do fact-based analysis to inform decision making," Armstrong said. "I think he brings that kind of approach to the quadrennial review. I'm not the least bit surprised that that's something he wanted to do."