(FORTUNE Magazine) – The much anticipated IPO of United Parcel Service is around the corner, and as you might expect, it's being led by a Wall Street giant--Morgan Stanley. But have you noticed the name of the other financial adviser handling the deal, Tanner & Co.?

Who?

Tanner & Co. is a 13-year-old Manhattan investment bank with exactly 12 employees, six of them bankers. But along with Morgan Stanley, Tanner is a main adviser to UPS on the IPO, which Wall Street sources estimate could raise $5 billion. That could add up to several million dollars in fees for tiny Tanner & Co. So how did this firm, which specializes in corporate financial advice and completes five to eight transactions a year, get in on what could be one of the biggest IPOs in history?

The short answer is Harold Tanner, the company's seasoned president. Tanner started his career back in 1956 at the white-shoe firm of Blyth & Co., and by the 1980s he was manager of corporate finance for Salomon Brothers.

Before joining Salomon, though, Tanner was introduced to several senior managers at UPS, and he soon began advising Big Brown. Tanner continued to work with UPS off and on over the years, both at Salomon and since he set up his own firm in 1987. Getting in on "the deal," the 67-year-old Tanner says, was an outgrowth of this history.

"We had discussed the possibility of going public with Harold many times, so it was a natural fit," says Robert Clanin, chief financial officer at UPS. "We've been private for 92 years, so we thought it would be nice to have someone who's been there."

--Angela Key