Antares Capital, led by Co-CEOS John Martin and David Brackett, has raised a collateralized loan obligation fund called Antares CLO 2017-1 Ltd marking the firm’s foray into CLOs. The fund will invest in leveraged loans to middle market private equity-backed companies.

The fund, which is valued at $2.1 billion, has received capital from banks, pension funds, insurance companies and asset managers. “This is a meaningful step in continuing to diversify our funding sources while providing investors access to middle market private debt, an increasingly attractive sector,” says Antares CFO Barry Giarraputo. The fund is the largest CLO raised in the U.S. since 2006, according to the Chicago-based firm. Antares expects middle market lending to pick up, thanks to a healthy M&A market.

Brackett and Martin offer a one-two punch as leaders of the most prolific middle-market lender in the U.S. They met at Heller Financial, the Chicago-based finance firm that rose to prominence in the ’80s and ’90s. They left Heller with about a dozen dealmakers in 1996 to launch Antares, with backing from Mass Mutual Life Insurance Co. In 2001, GE acquired Heller and then in 2005, GE bought Antares. As soon as GE announced it would sell GE Capital’s Sponsor Finance group in April 2015, a bidding war broke out with a long list of reported would-be acquirers. The winning $12 billion bid came from Canada Pension Plan Investment Board (CPPIB). Brackett and Martin won Mergers & Acquisitions’ 2015 Award for Dealmakers of the Year.

Other firms have been raising CLO funds. In 2016, the Carlyle Group (Nasdaq: CG) closed its fourth CLO fund at $507 million and Littlejohn’s Wellfleet closed a $406 million fund.