One reason why Satya Nadella, not Steve Ballmer, is Microsoft's CEO, according to an old rival

It's no secret that Satya Nadella has created a nicer and friendlier image for Microsoft since taking over as CEO last year.

In large part, Nadella has been able to do it by opening up the company to more partnerships, even teaming up with old foes like Salesforce and Box, which have often engaged in public, trash-talking events with Microsoft in the past.

In fact, Salesforce CEO Marc Benioff, who had been one of the most vocal critics of ex-Microsoft CEO Steve Ballmer during his tenure, thinks that's why Nadella was picked to replace Ballmer as head of the company.

"I think one of the reasons Steve Ballmer is not the CEO of Microsoft and Satya Nadella is [is] because Steve had a hard time having relationships with other CEOs," Benioff said in an interview on Bloomberg TV's Bloomberg "Go" Wednesday. "I know that from my personal experience, and Satya's the opposite."

Before Nadella came on board, Salesforce didn't do any meaningful work with Microsoft. If anything, Benioff would openly criticize the company for failing to go social or mobile under Ballmer's tenure.

But over the past two years, after Nadella's appointment, the two companies have been working closely together, announcing multiple collaboration deals, including a more tightly integrated Salesforce product with Microsoft's Windows devices and Office suite offerings.

Attracting talent

The two companies have grown so close that there were even reports of Microsoft possibly acquiring Salesforce earlier this year. Nadella, in fact, also became the first Microsoft CEO to ever hold a keynote speech at Dreamforce this year, the big annual user conference hosted by Salesforce.

Nadella's strategy to collaborate with others is also drawing more talented executives to Microsoft. Peggy Johnson, Microsoft's executive VP of business development, who also happens to be Nadella's first big hire, said she was convinced to join Microsoft last year because of his openness toward partnerships.

"I had watched his progression and I was curious about his vision. He seems so different. And out of the blue, when I got a call to look at the role as head of business development, and got to meet Satya in person - he's such a change agent," Johnson said in a previous interview with Bloomberg.

In the past year, Johnson has already been able to strike deals with Uber, Yahoo, and AOL. And she believes the list of partners will only continue to grow.

"Satya recognizes the importance of working with partners, so I think you'll continue to see perhaps surprising relationships in the year ahead," she said.