Slideshow 7 of PayPal's Biggest Rivalries

As PayPal has grown over the years, it has made enemies. Some of these rivalries were short-lived, while others persist to this day.

PayPal has a longstanding practice of cutting costs by urging consumers to fund their accounts via ACH transfers instead of card payments — and Visa is not happy about this. "What they do as a business is not good for us or for our clients," Visa CEO Charlie Scharf (pictured) said in a recent speech. "People talk about 'frenemies,' and there is no such thing in my mind. You are either one or the other."

When Apple Pay launched, PayPal was conspicuously absent from the long list of supporters. While PayPal told investors it was "hopeful" the two companies could come to terms, it was also engaged in a major marketing campaign slamming Apple's reputation in the wake of the infamous iCloud nude photo breach.

Before eBay purchased PayPal in 2002, the online marketplace developed a competing system with Wells Fargo called Billpoint. Though Billpoint was formed just half a year after PayPal launched, it couldn't catch PayPal's momentum, in part because Billpoint limited itself to eBay transactions and PayPal did not.

In its earliest years, PayPal ran afoul of New York prosecutors who did not want it handling payments for online gambling sites. PayPal agreed to a $200,000 settlement in 2002, shortly before finalizing its purchase by eBay, which officially cut the unit's ties to online gambling sites.

Over the years, PayPal has developed a habit of buying the companies it couldn't destroy through competition. These include Braintree, which reinvigorated PayPal's ailing relationships with developers; and Bill Me Later, maker of an instant credit offering that won the business of numerous online merchants.

Igor was the username of an especially hard-working con artist who bedeviled PayPal in its early years. According to PayPal co-founder Max Levchin, PayPal would not have survived if it did not find a way to outsmart Igor. The end result, unveiled in 2000, was some of the financial industry's earliest technology for monitoring online transactions. PayPal named this system "Igor" in honor of its old nemesis.

The concept of crowdfunding — wherein companies use sites like Kickstarter and Indiegogo to request funds for a product they have yet to release — didn't sit well with PayPal's fraud-screening and compliance rules. Thus, the crowdfunding community saw PayPal's policies as an impediment to the new business model.