Catholic philosopher, theologian, and author Michael Novak died Friday morning at his home in Washington, D.C. His daughter Jana Novak told The Washington Post her father died from complications related to colon cancer. He was 83.

Novak, who counseled both popes and politicians, was a scholar at the American Enterprise Institute for more than 30 years. In a tribute to his colleague, AEI president Arthur Brooks called Novak’s The Spirit of Democratic Capitalism, published in 1982, “likely Michael’s most important book.”

Brooks said it “advanced a bold and important thesis: America’s system of democratic capitalism represents a fusion of our political, economic, and moral-cultural systems. No facet can exist apart from the others.”

Novak’s most recent book, Justice Isn’t What You Think It Is (Encounter, 2015), written with Paul Adams and Elizabeth Shaw, continued that theme.

In addition to writing more than 35 books and his work with AEI, Novak served in the Reagan administration as U.S. ambassador to the UN Commission on Human Rights in 1981 and 1982 and was the recipient of the Templeton Prize for Progress in Religion in 1994. More recently, Novak was a visiting professor of business and economics at Catholic University of America in Washington.

Novak was predeceased by his wife of 46 years, Karen, who died in 2009. In addition to Jana Novak of Washington, two other children, Richard L. Novak of San Antonio and Tanya Holton of Boston, survive him, along with four grandchildren and a brother, Benjamin Novak of Ave Maria, Fla.