He’s a grandfather and longtime Washington suburbanite who now commands a powerful fighting force in northern Africa. He’s also a former CIA asset and anti-Islamist warrior who stands in the way of peace in Libya.

The United States and its allies can’t figure out what to do about Khalifa Hifter, the Libyan general whose refusal to support a fragile unity government has jeopardized hopes for stability in a country plagued by conflict.

Since he emerged as an important post-revolution figure in 2014, Western governments have struggled to define an effective policy to deal with Hifter, who has styled himself as an antidote to extremists while building his own power base and shunning the political process brokered by the United Nations.

“Hifter is threatening many of the Western-backed initiatives in Libya and the establishment of a recognized political power,” said Barak Barfi, a scholar at New America, a Washington think tank. “Hifter doesn’t have the strength on the battlefield to deliver on his promises to defeat Islamists, but he can act as a spoiler.”

Even as militia forces, backed by U.S. air power, make progress against the Islamic State in central Libya, Hifter looms as a primary impediment to White House hopes for restoring the democratic promise of the 2011 revolution that ended dictator Moammar Gaddafi’s long rule.