Most of the world’s challenges fit into three fundamental tugs-of-war, says Ajay Banga: that between the rights of “the one versus the many”; between the needs of humanity vs. the preservation of nature; and, finally, between short-term gains and long-term goals. The struggles are interconnected, like the sides of a triangle, Banga tells Fortune—and a good leader has to balance all of them. Arguably, few have managed that feat better than Banga, whose decade-plus at the helm of Mastercard has been a case study in fine-tuned corporate leadership. The stellar financials during his tenure—average annual profit growth of nearly 19%, a 40%-plus return on capital, and a total shareholder return approaching 1,600%—have come on the strength of (not in spite of) generous employee benefits and a commitment to community. Mastercard has ambitiously supported initiatives on environmental sustainability and is working to get a billion unbanked people around the world onto the financial grid—a legacy that ensures that Banga, who passes the CEO baton to Mastercard president Michael Miebach on Jan. 1, will be remembered as one who served the many.