Clayton Rein, a Twin Cities real estate developer and property manager who owned art galleries, pioneered the renting of artwork for corporate offices and founded a housing industry trade group, died in Scottsdale, Ariz., on Dec. 27. He was 99.

Rein was a supporter of progressive Democrats like Hubert H. Humphrey and his stance on civil rights in the 1960s. Rein ­carried that belief into business, resisting the era's real estate redlining practices, which excluded racial minorities from white neighborhoods, family members said.

"He was a great moral compass," said his oldest daughter, Judy Hoffman, who managed some of family's ­businesses.

In the housing industry, Rein promoted ethics, professionalism and training in property management. In the late 1960s, he and the newly formed Minnesota Multi Housing Association championed state legislation requiring landlords to pay interest on renters' security deposits.

"When he spoke, he stood tall and people listened," said Steven Schachtman, principal of Steven Scott Management of St. Louis Park, who launched his real estate career with mentoring help from Rein. "He had a vision that most people didn't have of housing that's affordable for people. He had the desire to help others."

In a 1994 profile of his business career, a Star Tribune columnist described Rein as someone "who literally qualifies as a rags-to-riches story." His father was a rag, paper and junk dealer in St. Paul, and Clayton Rein began doing the same in the 1930s.

That changed after World War II. Rein served in the U.S. merchant marine, and while at sea read a book about the value of property ownership. After the war — and just in time for the postwar housing boom — he set up a real estate business in St. Paul.

"I didn't know a thing about the real estate business, but when you're in your 20s, you know it all," he once said.

His company, C.G. Rein Co., first sold homes, then shifted to developing, owning and managing apartments and other buildings. At its peak in the early 1980s, the company owned 1.5 million square feet of commercial property, including shopping centers and tennis clubs, and 2,200 apartment units in the metropolitan area.

In 1967, he founded the Minnesota Multi Housing Association and served as its first president. It now represents 2,100 owners and managers of rental housing. "He was the sparkplug who had the idea and concept and got others involved," said Mary Rippe, its current president.

Rein also collected art, a passion that he turned into a business in the late 1970s. He opened galleries in several cities, including Edina and Scottsdale, and also rented artwork to hundreds of U.S. corporations to adorn their offices.

He called himself a social liberal and a fiscal conservative. He was a supporter and friend of Gov. Karl Rolvaag, working with him in 1965 when Minnesota hosted the National Governors Association's annual conference, said his daughter, Trish Cowle, who also was an executive with C.G. Rein Co. Rein was an alternate delegate to the 1964 Democratic convention in Atlantic City, N.J., when Humphrey was nominated as the vice presidential candidate on the ticket with President Lyndon Johnson.

Rein began winding down his ventures in the 1990s and sold most of the remainder in the 2000s, and had lived full-time in Arizona for about a decade.

He is survived by his wife, Virginia, who worked as the company's bookkeeper and treasurer throughout Rein's career, and two other children, Burt Rein and Stan Rein; nine grandchildren; and 12 great-grandchildren.

A Minnesota memorial service is planned in early spring.