The most influential name in activist investing you've never heard of crushed it in 2015 (GS, jpm)

REUTERS/Eduardo Munoz

There is a big name in activist investing that has been involved in more than 70 campaigns so far this year.

It isn't Pershing Square, Icahn Associates, or Third Point. You've probably never heard of it.

It's Wall Street law firm Olshan Frome Wolosky LLP.

The law firm ranks as the top activist legal adviser, working on 74 campaigns so far in 2015, according to new data from Activist Insight.

That is more than three-times the number of campaigns second-placed Schulte Roth & Zabel has worked on.

The firm is the go-to legal adviser for many of Wall Street's biggest and most successful activists. It has worked for clients including Jeffrey Smith's Starboard Value LP, along with Lone Star Value Management and Glenn Welling's Engaged Capital LLC.

The law firm's activity in activism appears to be growing as the strategy is becoming increasingly popular with investors.

Steven Wolosky, a partner and chair of the activist- and equity-investment practice at Olshan, told Business Insider in August that most of his clients are focused on operational activism rather than turning a quick buck.

Activists are now acting almost like private equity firms, performing diligence on a deal and looking to market their viewpoints to institutional investors, he said.

"It's beyond the performance of the company," said Wolosky. "It's beyond the CEO's performance."

REUTERS/Eduardo Munoz

The rise in activism has placed a premium on legal expertise. Hedge funds and big banks alike are eager to bring experts into their ranks to ready defenses in increasingly costly campaigns to control boards' independence.

Ex-activist lawyer David Rosewater signed on with Morgan Stanley in April to head the activism defense practice, and another ex-lawyer teamed up with a former JPMorgan executive to launch an activist fund focused on collaborative management earlier this year.

And Bill Ackman's Pershing Square Capital fund hired ex-Kirkland & Ellis lawyer Stephen Fraidin in January after the M&A pro spent more than a decade on the hedge fund's advisory board.

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