Not all entrepreneurs need co-founders, but many successful companies -- including Apple, eBay, and Twitter -- were built by multiple leaders with productive relationships. 

How did these individuals find their business counterparts? And what made their combined skill-sets a recipe for success? 

Not surprisingly, many were long-time friends, classmates, or relatives.  Others, however, did not get along initially. Some still are not amicable, despite their joint achievements.

There is a common trend: the most well-rounded pairs recognized their individual limitations and respected what the other could bring to a partnership.  Many of these duos have gone on to run some of the most successful businesses of our time.