If Time Warner is folded into AT&T, it will mark the end of an era, for both an executive who rose through the corporate ranks after starting as an HBO staff member in 1979 — using a stack of boxes as a desk — and a media conglomerate. Over the past century, dating to its roots in Time Inc., the company ushered in a series of innovations, including the first talking feature film, the first premium cable network, the first 24-hour news network and, on Mr. Bewkes’s watch, a push toward video-on-demand and other digital offerings.

“It is the legacy that I have been the steward of,” Mr. Bewkes, 65, said. “That is why we thought, ‘We have got to do the next step.’”

In an industry filled with larger-than-life executives, driven to expand their empires, Mr. Bewkes developed a reputation as a cerebral, private figure with a dry sense of humor, who was focused on creating value for investors. He did so by spinning off Time Warner Cable in 2009, AOL the same year and the Time Inc. magazine division in 2014.

What was left was a focused TV and film company. Mr. Bewkes invested in ambitious programming, including original series on HBO like “Game of Thrones,” sports deals like the N.C.A.A. basketball tournament and big bets on major film franchises like the “Harry Potter” movies and the “Lord of the Rings” trilogy.

He also pushed toward a streaming future, evangelizing his “TV Everywhere” video-on-demand initiative and creating HBO’s stand-alone streaming service.

As a result, Time Warner was positioned as an attractive takeover target.

Mr. Bewkes’s success can be attributed to “being very, very rational in his decision making and, on the other hand, having a real flair for the creative,” said Michael Lynton, a longtime media executive who was at Time Warner when it merged with AOL. “That is a rare combination.”

There is no question that Mr. Bewkes has delivered value to shareholders. A $1,000 investment in Time Warner stock when he became chief executive in 2008 would be worth about $4,400 today.