UPDATED: September 22, 2012, at 1:58 a.m.

James L. Medoff, a respected Harvard economics professor and an expert in the role of unions in the American economy, died Saturday in Chelsea, Mass. He was 65.

Medoff, who passed away due to complications resulting from multiple sclerosis, arrived at Harvard after graduating from Brown in 1969 and never left—finishing a masters in economics in 1973 and a doctorate in the same field in 1975. He later earned tenure as the Meyer Kestnbaum Professor of Labor and Industry.

An influential voice in the field of labor economics, Medoff wrote his first book “What Do Unions Do?” in 1984 with friend and fellow Harvard professor Richard B. Freeman. It was a landmark work in their field, challenging common prejudices against unions and defending the organizations that their colleagues often criticized.

Medoff also advised companies such as IBM, The Boston Globe, and Ford Motor Company, and was a consultant for major unions including the National Association of Letter Carriers. He was considered an expert on the complicated collective bargaining issues that U.S. Postal workers face with government administration, and in 2004, testified before a Presidential Commission looking into the organization.

While much of this work took Medoff away from Cambridge, he always felt at home at Harvard and rushed to return to teaching, according to his son Justin Medoff.

“As soon as he arrived in Cambridge he just felt privileged to be there, to be a part of the Harvard community,” Justin said. “He wanted to contribute anything he could.”

His students recognized this dedication to the College and were especially drawn to his flamboyant and energetic lecturing style, said Economics concentration adviser Kiran Gajwani. She continued that Medoff’s courses were often some of the most popular in the department.

“He always said that he thought people would remember something, would understand something better if it was explained with energy,” Justin added.

“He tried to bring that energy—that flamboyance—to the classroom.”

Medoff was known for his wit and love of good humor inside and outside of class. According to Tyler B. Goodspeed, one of Medoff’s students and later his research assistant, there were always two tasks that Medoff took very seriously in his first class of the term. The first was to find volunteers to kick off his lecture with a joke. The second was to collect each of his students’ phone numbers, so he could call each personally.

“Yeah, he would call them,” Justin said. “That was a big thing with my dad, a commitment to work and to family.”

Medoff brought the same engagement and enthusiasm to his role as a father.

“Anything I got interested in, he’d get interested in, so we could do it together,” Just said. “We’d go to card shows, baseball games—any level, minors, college, whatever—and just be together.”

In addition to his son, Justin, Medoff is survived by his sister Joanne Darman Medoff and by his daughter Susanna, who graduated from the College in 2008.

“Having Susanna at Harvard, my dad was really, really proud of that,” said Justin. “He really enjoyed that.”