Dan Amos, Aflac's CEO since 1990, has joined the ranks of the top 100 CEOs in the world, according to the Harvard Business Review (HBR).

The publication puts out an annual list ranking the world’s "best performing CEOs," but this year the criteria changed slightly.

In previous years the list has essentially mimicked each company's stock price with the best performing stocks equaling the best performing CEOs. That's no longer the case, however, because HBR decided to include other influences, most notably corporate social responsibility (CSR).

While Aflac has seen annual revenues increase from $2.7 billion to nearly $23 billion since he took over as CEO, the company's sustainability record also played a part in Amos' inclusion on the list at number 69.

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"Aflac internalizes CSR from the top down better than any company I know of. Dan takes it personally," says Jon Sullivan, a member of Aflac's corporate communications team. "He doesn't just write a check or ask others to write a check, Dan feels it in his soul. He is frequently attending events at the Aflac Cancer Center and meeting with children and families, and when he is there, he seems to have time for everyone."

Amos initiated the company's sponsorship of the Aflac Cancer Center in Atlanta, a relationship that has spanned 20 years. In fact, Aflac recently announced it has surpassed $100 million in donations since the partnership began.

"Dan takes helping kids with cancer personally, and he wants his company to reflect that," says Sullivan. "He is a first-rate CEO, but he's a better person."

Aflac CEO Dan Amos attends a Fukushima memorial service following the 2011 tsunami.Aflac CEO Dan Amos attends a Fukushima memorial service following the 2011 tsunami. (Photo: Aflac)

Amos was a key figure in crafting the now-famous marketing campaign using the Aflac duck, which raised the company's brand recognition from the single digits in 1999 to more than 95 percent today. One of the things Sullivan said he admires most about Amos is his willingness to do the right thing, no matter what the cost.

After a devastating tsunami hit Japan in 2011, comedian Gilbert Gottfried—and the voice of the Aflac duck—tweeted offensive comments about the victims. What would Amos do about the voice of one of the most recognizable mascots in America?

"When he heard the comments, Dan fired Gottfried within an hour. He did that in spite of the fact that Gottfried had voiced all of our television commercials," Sullivan says. "In essence, firing Gottfried silenced the Aflac Duck. But for Dan, that didn’t matter. He offended our customers and the people of Japan. It was the right thing to do."

Amos' leadership has helped land Aflac on Fortune Magazine's list of the Best Companies to Work For 17 years in a row. It's also the only insurance company to have been on Ethisphere's list of the World's Most Ethical companies every year since the award began in 2007