NEW YORK (

TheStreet

) -- Bill Ackman's exit from

J.C. Penney's

(JCP) - Get Report

board of directors isn't a death knell for activist investing.

Ackman's departure from J.C. Penney comes after his hand-picked CEO Ron Johnson failed to turn around the struggling retail giant, and the hedge funder waged a losing war over the company's management and strategy. Many now wonder whether J.C. Penney can make it past the holidays, after spending billions on a failed store revamp that drained the company's cash coffers.

J.C. Penney elected retail industry veteran Ronald W. Tysoe, the former vice chairman of what is now

Macy's

(M) - Get Report

, to the company's board on Tuesday, a move Ackman said he supports.

The hedge funder's retreat at J.C. Penney comes as his nemesis, Daniel Loeb of

Third Point Capital Management

, was forced by Hollywood icon George Clooney to backtrack from highly critical comments he made to

Sony's

(SNE) - Get Report

management. Loeb owns about $1 billion in Sony shares and seeks to spin off the company's movie studio business in an attempt to revive the struggling electronics giant.

Carl C. Icahn, the dean of modern day activist investing, meanwhile, faces the imminent prospect of failing to win over

Dell

(DELL) - Get Report

shareholders on a competing bid to what could be one of the biggest leveraged buyouts in history.

Ackman, Loeb and Icahn are all intimately connected to a drama at

Herbalife

(HLF) - Get Report

. Ackman has bet $1 billion that the company is little more than a Ponzi scheme. Loeb and Icahn have publicly taken the other side of Ackman's trade and have, so far, made millions of dollars in profit. "New HLF product: The Herbalife Enema administered by Uncle Carl," Loeb wrote on his

Bloomberg

profile in July.

Clearly, a crass breed of barbarians is storming the gates of Corporate America. What board would let them in?

The answer is that while Ackman, Loeb and Icahn may be pushing the limits of good judgment, they will continue to have a significant influence on markets.

Ackman, after all, remains an independent director on

Canadian Pacific's

(CP) - Get Report

board. Meanwhile, the hedge funder has recently made a play at chemicals giant

Air Products

(APD) - Get Report

. Loeb can count a turnaround at

Yahoo!

(YHOO)

under new CEO Marissa Mayer as a major recent activist success.

Loeb, at times, resorted to crude tactics such as publicly shaming Yahoo!'s former CEO Scott Thompson. With hindsight, the company's shareholders are likely to view such actions as necessary.

Carl Icahn helped to pull

Chesapeake Energy

(CHK) - Get Report

from the brink of bankruptcy after building an investor consortium on the embattled oil and gas driller's board. Analysts see Icahn's influence as helping impart Chesapeake's management change and its execution on needed asset sales and capital expenditure reductions.

Lessons Learned

Still, Ackman and Loeb are likely to consider recent setbacks at J.C. Penney and Sony as a learning experience. If either hedge fund manager considers changing their tactics, there are others to follow who play a less-heralded but similarly influential role on investments.

Jeffrey Ubben of

ValueAct Capital Management

, while generally media shy, may be the activist to watch

this year

. Quietly, Ubben and ValueAct have won board seats and supported drastic changes at firms such as

Adobe

(ADBE) - Get Report

and

Valeant Pharmaceuticals

(VRX)

that are paying off for shareholders.

ValueAct may be on the verge of its most impressive activist investments yet after taking a large position in

Microsoft

(MSFT) - Get Report

shares earlier in 2013. While Microsoft is the dominant player in PC-software, its earnings outlook has become clouded by a string of failed attempts to enter the smartphone and tablet markets.

Ubben told

TheStreet

in 2012 that he liked to work with management in so-called activist investments and has recently pushed for firms to consider

mergers and acquisitions

. Microsoft may presently be in need of a transformative acquisition and the company is consistently speculated as an acquirer.

In the health care sector, Larry Robbins of

Glenview Management

operates in a similarly understated manner, even if the hedge funder has assembled a multi-billion dollar bet on the

consolidating health care sector

. On Monday, Glenview won a shareholder vote to take full control of

Health Management's Associates

(HMA)

board of directors as they seek a

higher share price

to

Community Health Management's

(CYH) - Get Report

near $4 billion bid for the company.

Like Ubben, Robbins can be described as an "activist" investor; however, he prefers the notion of being a "suggestivist" who works with management in most cases. Shareholder votes such as the one conducted at Health Management on Monday indicate Robbins' style has a high degree of credibility with investors in the health care sector.

For the average U.S. wireless subscriber, no hedge fund investor may have a bigger impact on their pocketbooks than John Paulson of

Paulson & Co.

.

After taking up

large holdings

in struggling wireless players such as

Sprint

(S) - Get Report

and

MetroPCS

(PCS)

, the fund is poised to benefit the most from a consolidation among also-rans in the industry.

Paulson & Co. also added a voice of reason in the wireless industry's consolidation, after advocating lower debt levels in

T-Mobile's

(TMUS) - Get Report

acquisition of MetroPCS and helping to halt an escalating bidding war for Sprint. In both instances, leverage was a big issue holding back their

price competition

against

AT&T

(T) - Get Report

and

Verizon

(VZ) - Get Report

.

What's Next

.

It may be hard to teach an old dog like Icahn new tricks in investing and the billionaire activist has brushed off many failures in his career. Ackman and Loeb, however, may still be learning how to execute big investing ideas such as J.C. Penney and Sony. If they do fail to turnaround both firms, it may simply lead to a change in their style.

Activist investing may take a big hit this summer, but don't count these guy's out.

-- Written by Antoine Gara in New York

Follow @antoinegara