Gregg Lemkau was always a bit of a geek, but he learned to hide it early. “He’d be reading a comic book or some light magazine, and inside it would be a textbook,” recalls former Dartmouth College head soccer coach Bobby Clark of the young Lemkau, who played goalie for a team that made it to the National Collegiate Athletic Association’s Division I quarterfinals in 1990. Although Lemkau was studious, Clark adds, he competed hard and never stopped smiling.

Those qualities have served the father of four well. In September, Goldman Sachs Group named London-based Lemkau head of mergers and acquisitions for Europe, the Middle East, Africa and Asia-Pacific. He previously co-led the technology, media and telecommunications division with George Lee; Anthony Noto has succeeded him in that role. Lemkau, 42, left the post on a high note: This year Goldman ranks first in the TMT sector, with $107.6 billion in deal volume through mid-October, according to Dealogic — a 39 percent jump over the whole of 2010, when the firm ranked sixth.

Among other 2011 deals, Lemkau has advised U.K. software maker Autonomy Corp. on its $11.7 billion takeover by Hewlett-Packard Co. and private equity firm Silver Lake Partners on its $8.5 billion sale of online phone service Skype to Microsoft Corp. In a fundraising effort for Palo Alto, California–based Facebook, he helped Mark Zuckerberg’s social network secure $1.5 billion.

Lemkau describes his work as highly stimulating. “Every person you have the chance to interact with in this job is great at what they do,” he says. “It helps make you better at what you do, builds great experience and forces you to be on the top of your game.”

That includes jawing with clients like Russian Internet tycoon Yuri Milner, an investor in Facebook and founder of Hong Kong–based DST Global, whom Lemkau advised on the $5.7 billion initial public offering of Mail.ru Group last year. “We had a very profound conversation about the trends and the space,” the billionaire says. “Gregg’s extremely professional and knowledgeable about the Internet.”

At Dartmouth the Boston-born Lemkau planned to pursue a legal career. After graduating in 1991 with a degree in economics and government, he joined a leading law firm as an M&A paralegal. But his friends’ lives in banking appealed to him more, so the following year he started at Goldman as an analyst.