The check-writer is Ed Conard, who was a top official at Bain, the private-equity firm Romney helped create, and who has been a strong supporter of his over the years.

The donation, made to the super PAC “Restore Our Future” - which was founded by former Romney advisers and is able to take in unlimited contributions, but must report them to the FEC - showed up in the group’s first round of filings. It was listed as coming from a W Spann LLC.

In a statement to POLITICO, Conard said, “I am the individual who formed and funded W Spann LLC. I authorized W Spann LLC’s contribution to Restore Our Future PAC.

“I did so after consulting prominent legal counsel regarding the transaction, and based on my understanding that the contribution would comply with applicable laws,” he said. “To address questions raised by the media concerning the contribution, I will request that Restore Our Future PAC amend its public reports to disclose me as the donor associated with this contribution.”

The LLC had been registered to a Madison Avenue address in Manhattan that was the same building occupied by Bain, sparking more of the mystery surrounding Spann. Sources familiar with the situation said Conard retired from Bain in 2007, but still maintains an office of his own at that Madison Avenue address.

Conard came forward as criticism from campaign watchdogs and Democrats were gathering steam, and there was an official complaint with the FEC, as well as with the Justice Department, filed by a nonpartisan group.

The contribution was first reported by POLITICO’s Jonathan Martin and Ken Vogel on Sunday. NBC’s Michael Isikoff reported earlier this week that Spann was formed in March and dissolved less than four months later, raising questions about the purpose of the company.

It wasn’t immediately clear why Conard chose to go the anonymous donation route.

Based on his donation history and his past with Romney, at first glance there may be less there than meets the eye in terms of a hidden political agenda. Conard has no major history as a Republican donor, and is not a known name within bundler circles.

He’s made a few donations to the Republican National Committee, and contributed to George W. Bush’s and Massachusetts Sen. Scott Brown’s campaigns, but the overwhelming majority of his donations have been to Romney and his two PACS, Commonwealth PAC and Free and Strong America.

He is among a group of Romney supporters who has donated to the network of the state-based versions of the PACs, which can have higher contribution limits.

Among his few political media appearances was in 2007 during Romney’s last race, described as a major supporter.

UPDATE: Restore Our Future spokeswoman Brittany Gross said in a statement, “We’re glad Mr. Conard has chosen to come forward putting an end to this supposed controversy. Restore our Future will amend our report per Mr. Conard’s request to reflect him as the donor.”