Activist investor Carl Icahn is no shrinking violet.

The investing public has watched as Mr. Icahn has waged highly publicized campaigns against the likes of Apple, Dell, and many more over the years. And while he might not always achieve his ultimate goals, his returns are hard to overlook. According to one source, Icahn's 2013 activist campaigns alone on average generated a 40% annualized return for those investing alongside him.

More recently, Icahn has set his sites on online auction dynamo eBay (EBAY -2.91%) for his next high profile crusade. And this week, he escalated his attack on eBay by shifting his focus to another aspect of its business – its directors.

eBay vs Icahn – Round 1
Late last month, Icahn announced he had established a 2% stake (around $1.5 billion) in the online auction company along with a call for eBay to spinoff its highly coveted online payment processing unit PayPal. He further maintained that he was ready for yet another proxy fight against eBay in hopes of landing two board seats for his representatives as well. 

Source: Twitter

eBay's management team quickly rebuffed Icahn's proposal, as it has with the multitude of other financial analysts that have lobbied in favor spinning off PayPal over the years. eBay CEO John Donahoe quickly took the eBay's corporate blog to defend his position, arguing unsurprisingly that "we continue to believe that the company, our customers, and our shareholder are best served by keeping PayPal and eBay together." 

Donahoe returned to the consistent argument in favor of keeping eBay and PayPal under a single corporate fold, namely that eBay and PayPal offer to strong of synergies to merit their separation. And while synergies have been used as the rationale for more bad corporate deal-making than perhaps any other, it certainly makes sense that an auction company like eBay, where lots of commerce takes place, could make a disproportionate amount of money by funneling the payment for those auctions toward a payment company is too owns.

However, this explanation failed to satisfy the likes of Carl Icahn who chose to pursue a different tactic in his next attempt to cajole eBay into action.

Round 2: Mudslinging
Apparently unsatisfied with his lack of progress, Icahn published three open letters this week decrying the behavior of eBay's board of directors.

Icahn's criticism focuses on the board's activity with two of its own – venture capitalist Marc Andreessen and Intuit (INTU 0.18%) founder and board memeber Scott Cook. To be fair, Icahn raises several interesting issues regarding the boards behavior.

Regarding Mr. Andreessen, one of the most widely admired venture capitalists in the business, Icahn calls into question the circumstances surrounding eBay and Mr. Andreessen's dealings with Skype. Mr. Andreessen became an independent director on eBay's board in September of 2008 , nearly found years after eBay acquired Skype for $2.5 billion . One year later in September of '09, a group of investors including Mr Andreessen's VC firm Andreessen Horowitz agreed to acquire 65% of Skype from eBay in a deal that valued the online calling platform at $2.75 billion. Then in mid-2011, Skype was ultimately sold to Microsoft for a whopping $8.5 billion.

It's easy to see how one could call into question the intimate and highly profitable involvement Mr. Andreessen had with the multiple Skype deals. And, it's this fact seeming conflict of interest that has Mr. Icahn crying afoul. In his eyes, Andreessen made huge sums front-running an inevitable acquisition of Skype, costing eBay investors billions in potential gains.

In the case of Mr. Cook, Icahn notes that Intuit and PayPal compete nearly directly. Mr. Cook is the fourth largest shareholder at Intuit, where his 4.65% at the end of last year was worth a whopping $1 billion. Icahn cites PayPal's PayPal Here product contends directly with Intuit's GoPayment product. He claims, also understandable, that Cook's access to PayPal's intimate operational details could provide a meaningful advantage for Intuit in market where the two compete and the potential for meaningful monetary gain for Mr. Cook.

Moving on to the middle rounds
Mr. Icahn certainly raises some fair questions with these letters, although no one has accused either Mr. Andreessen or Mr. Cook of any wrongdoing in relation to their activities as eBay board members. Cleary, the matchup between Icahn and eBay's board is in the early innings, so expect more fireworks in the weeks to come.

However, whether or not Mr. Icahn will be able to effect any real change at eBay remains far from a sure thing today.