Robert A.G. Monks was a big man in nearly every sense.

A pioneer of shareholder activism and good corporate governance, Monks stood about 6 feet, 6 inches tall and carried a great sense of humor and an even greater love for people, his son Bobby Monks said. The elder Monks was “imaginative and creative — and a lot of fun to be with,” his son said.

Robert Monks, who was born in Boston but built his legacy largely in Maine, died April 29 in his Cape Elizabeth home. He was 91.

During a decades-long career as a lawyer, venture capitalist, author and leader of companies that spanned finance to oil and coal, Monks helped shape the modern corporate landscape. He championed the power — and emphasized the responsibility — of individual shareholders in steering public companies.

“Monks dedicated his life to challenging entrenched corporate power structures and championing the rights of shareholders, leaving an indelible mark on both the business world and public policy,” his family wrote in his obituary.

Monks authored numerous books on corporate governance. He founded Institutional Shareholder Services and ValueEdge Advisors, among several other companies, which hold board members and executives accountable to the values and ethics of shareholders while also stewarding long-term financial growth.

In the preface of his final book, “The Emperor’s Nightmare: Saving American Democracy in the Age of Citizens United,” published in 2022, he argued that the fundamental goal of nearly any corporation is the pursuit of unlimited size and power. “This aspect of the corporation makes it a kind of rogue leviathan,” which appears to be alive but lacks human emotion and empathy and must be guided by considerate shareholders — or, as he increasingly believed in his later life, robust federal law.

“He was a pioneer in that area,” Bobby Monks said. “It left a big impact. It’s sort of embedded in our culture now.”

Nathan Szanton, a longtime friend and business partner of Bobby Monks, said shareholder activism was “a radical notion” at the time.

“The core of the idea is that the shareholders own the company. They are the owners. Not the board and not the CEO,” Szanton said. “Someone had to kind of come along and say, ‘Wake up people. We have power.'”

Bobby Monks said his father was generally more interested in starting companies and fostering their initial growth before stepping back than he was in growing any one venture.

“He wasn’t somebody who grew companies,” he said. “He wasn’t really interested in that. He was interested in the next idea.”

Beyond his contributions in the private sector, Monks was appointed Maine’s energy commissioner in 1975, served as a founding trustee of the Federal Employees’ Retirement System and, from 1983 to 1985, oversaw the country’s pension system as administrator of the Office of Pension and Welfare Benefits Programs at the Labor Department, his family wrote.

“I think he’d be happy right now with what he achieved. He was a very positive guy, even in the face of things that were really difficult,” Bobby Monks said.

He pointed as an example to his father’s three campaigns for the U.S. Senate: challenging incumbents Margaret Chase Smith in the 1972 Republican primary and Edmund Muskie in the 1976 election, and in running in the primary against Sen. Susan Collins before she was elected to the Senate in 1996.

“You have to have a degree of optimism to believe that you’re going to win,” Bobby Monks said with a laugh.

Though Monks ran as a Republican in all three races, his relationship with the party shifted as he aged. When Barack Obama first campaigned for the presidency in 2008, Monks co-chaired a “Republicans for Obama” initiative, at times opening his door to the then-Senator, the New York Times reported more than a decade ago.

At 19, Monks married Millicent Carnegie Sprague, a granddaughter of Thomas Carnegie, younger brother of industrialist Andrew Carnegie, his son said. The pair spent much of their lives on the Maine coast. She died in 2023 after 69 years of marriage.

They had their first child about two years after marrying, a daughter named Melinda, and Bobby Monks arrived two years after that, he said. At times, people said the two men looked more like brothers than father and son, Monks said.

“Well, we grew up together,” Monks recalled his father’s usual response.

At home, Monks was a caring and present grandfather of three and great-grandfather of six.

“We’d go over for dinner there once a week, and they’d spend time with them,” Bobby Monks said. “He was good to them.”

He grew more interested in others than himself as he aged, especially his great-grandchildren, his son said.

“He had a really innate ability to be able to listen to what people had to say,” Bobby Monks said. “If you ever failed at something and you walked into his office, you’d walk out thinking you’d succeeded.”

Szanton said that while he only met Robert Monks — whom family and close friends called “Big Bob” — a handful of times, the older man had undeniable charm.

“Just a big booming voice, a great big smile, very welcoming, very good at putting people at ease, clearly super bright,” Szanton said. “If he was in the room, you absolutely knew.”

In the days since his father’s death, Bobby Monks said he’s received an outpouring of support, including stories of his father’s generosity that he had never heard before.

“There were times that he just paid for people’s schooling, for example, that I just didn’t know about. He just never told me about them,” Bobby Monks said. “People that I know quite well.”

That generosity is a key part of Monks’ legacy, his son said, adding that he influenced countless others, from those he personally supported to others who simply read his work or believed in his same ideals.

“In the corporate governance movement, he was sort of the senior guy for a while. … That world will miss him,” Monks said. “He will certainly be missed by his family. He was such a fun person to be with.”