D. William Brosnan was a president of Southern Railway in the USA, a railroad that later merged with Norfolk and Western Railroad to form Norfolk Southern Railway. He succeeded Harry A. deButts in 1962. In 1964 Brosnan was selected as the first recipient of the Man of the Year award by Modern Railways magazine, an award now presented by Railway Age magazine as the Railroader of the Year.

While Brosnan was a brilliant railroader and innovator, his ham-fisted tactics of management, specifically during the takeover of the Central of Georgia Railroad in 1963, forever marked him as a ruthless tyrant to many. For many years after Brosnan was gone one could not find any former Central of Georgia (and very few Southern) agreement employees who would speak of him in printable language. Nearly 1,500 employees of the Central were terminated without cause on Brosnan's orders after the merger. Four years later, a Federal Court ruled that the Southern had to pay retroactive pay to these unfairly terminated workers.

Brosnan, for all of his innovations, was very shortsighted in some areas of the company business. He would spend millions of dollars on a new centralized computer office, while draining the railroad dry of much needed funds to maintain the very livelyhood of a railroad; it's track! On some divisions, multiple derailments each day were commonplace due to decrepit track, and complaints from both customers and board members poured in. Despite this, he was the pioneer of mechanized track machines and other railroad innovations that saved the company money.

Brosnan also fired the opening salvo against the Interstate Commerce Commission in the "Big John" grain hopper case that would ultimately lead to the Staggers Rail Act of 1980 and the eventual dissolution of the ICC in 1996. He is also responsible for many modern day ideas including the unit train and remote control locomotives.

In 1967, Brosnan was informed by Southern's board of directors that he would have to step down as Chairman and CEO of the Southern Railway, using his own edict against him which mandated retirement at age 65. By this time, he had ruffled the feathers of almost everyone on the board of directors. That, coupled with the fact that he was spending less and less time actually managing the railroad led to the board members pushing for his retirement. Many of his heavy-handed, military style management tactics can still be found on the current Norfolk Southern system.

He remained on the board of directors of the Southern until 1983. Brosnan died in 1985.