This past October, thousands of people lined up to run the Chicago Marathon despite the record temperatures. About three-and-a-half hours into the 26.2-mile race, organizers stopped it because the 90-degree heat was making it dangerous for runners to continue. Hundreds of runners were halted, but by that time Jeff Rosenkranz, who in September became head of the mergers-and-acquisitions group at Piper Jaffray, was just about to cross the finish line.

“It was incredibly hot, but I survived it,” says the 44-year-old Rosenkranz. “There was no way I was quitting.” And it is with this tenacity that Rosenkranz has approached his 22-year career as an investment banker, spending the majority of that time focused on the middle-market deals for which Minneapolis-based Piper Jaffray has become best known.

“He is an undying advocate for his clients. He won’t give up, which is a quality you want in someone who is selling your business,” says Charles Hanemann, a managing director at H.I.G. Capital whom Rosenkranz has advised in the past. “But he is also honest and fair.”

While many bankers chase the dollars and the glory of the large, headline-grabbing deals, Rosenkranz has always been most comfortable doing the smaller transactions that make up the vast majority of M&A deals.

“Ninety-five percent of the M&A activity is generated from deals that are worth below $1 billion and those deals are just more interesting,” Rosenkranz says. “These are the people who are actually making business happen, as opposed to the large market, where you’re working with someone who’s [in turn] working with someone who’s making business happen.” Middle-market companies, he adds, “usually need the help when they are selling their business and welcome the advice.”

As an example, Rosenkranz describes how he recently helped two private equity firms sell their stakes in a medium-size manufacturing company that makes disposable gloves. After researching the company, Rosenkranz concluded that its C.E.O. did not have a long-term commitment to stay with the company. The P.E. firms wanted to sell quickly anyway, but Rosenkranz managed to convince them to wait and instead prepare the company’s second-in-command, who did want to stay with the firm, for the top spot. Doing this delayed the sale by more than four months, but made for a much more attractive deal down the road.

“It slowed the process down, but I didn’t want to immediately go to market with this situation,” says Rosenkranz. “We really needed to advise our clients and manage the changes taking place before this company was sold.”

Rosenkranz’s straightforward, no-nonsense personality is a good fit with the types of deals he’s working on and the kinds of people he’s dealing with. In the M&A world, where a limited number of private equity firms are now doing most of the buying and selling, building long-lasting solid relationships is the key to success, and Rosenkranz excels at this. Case in point: The private equity firms that owned the disposable-glove company had initially come to him for counsel more than five years ago, at which time Rosenkranz advised against the sale because he felt market conditions were not favorable. But when they wanted to sell again last year, the first person they sought out was Rosenkranz.

“Jeff is practical and honest—he’ll let us know if we’re wasting our time chasing something that’s not going to work,” says Chris Perry, a partner with CIVC Partners, a middle-market buyout firm with more than $1 billion under management. Rosenkranz advised CIVC earlier this year on both its purchase of repair-service firm Precision Camera and its sale of contract-cleaning-services firm Kellermeyer Building Services to another private equity group.