Brad Cleveland, a computer scientist and even-keeled executive who helped turn Proto Labs into one of Minnesota’s leading technology companies, has died of brain cancer at the age of 56.

Cleveland, who had battled brain tumors for years, retired from the Maple Plain company in early 2014. He died Sunday.

“We will remember Brad for his caring and generous nature,” his wife, Pat Cleveland, wrote in an e-mail.

Cleveland joined Proto Labs inventor Larry Lukis in 2001. Cleveland recruited private investment to fund its growth and took Proto public in 2012.

By 2013, the Maple Plain-based outfit had 750 employees at plants around the Twin Cities and the globe.

In late 2013, as Proto Labs neared $150 million in profitable revenue and a market value of $2 billion, Cleveland decided to turn the helm over to a new leader as he focused on his health, travel, a fledgling alternative energy businesses and a family foundation.

“We were a great team,” said Lukis, 68, the founder and chairman of the internet-enabled maker of prototype molds and parts for global manufacturers. “I did the technical work. Brad built the company. He was organized. We developed a strategy and he knew how to execute.

“He always looked to advance our people. There are people who started polishing molds and became managers. Brad said, ‘Let’s bet on these people. Let’s bet on growth.’ He was always, even in the early years, paying everybody bonuses.”

CEO Vicki Holt, who replaced Cleveland in 2014, told employees Monday: “The Proto Labs family has lost a tremendous business leader and truly amazing person. Brad led the company’s transformation from a small injection molding start-up to a global technology-enabled, digital-manufacturing company. We are incredibly grateful …”

Vinny Vassallo, a St. Paul-based limousine company owner, recalled that Cleveland hired him 20-plus years ago to work in a factory that Cleveland ran for MTS Systems. He eventually promoted Vassallo to shop manager.

“He didn’t have a big ego,” recalled Vassallo. “He became a good friend. He took a bunch of us, old MTS people, his brother, his son, three years ago, fishing in Alaska. The airfare, the resort, the guides, the meals — Brad paid. It was the trip of a lifetime. Brad’s tumor made him sick, but he didn’t mention it.

“He told me that as long he was alive, he wanted to see people enjoy things.”

Vassallo said he told Cleveland in the late 1990s that Cleveland probably was overpaying him. “Brad said I was worth it,” said Vassallo. “Production had quadrupled. He was the best guy I ever worked with.”

Cleveland borrowed $600,000 to invest in Proto Labs in 2001. He was worth tens of millions in stock by 2013. He built a new house in the western suburbs and a vacation home in Wisconsin. He invested in new businesses. And he donated millions to health care and other causes.

Cleveland was a champion of the Minnesota Cup entrepreneurial sweepstakes which conducts its annual awards ceremony at the University of Minnesota on Sept. 22. “Activated Research,” a fuel cell technology initiative funded by Cleveland and Andrew Jones is the winner of the energy division. Jones is a chemical engineer whom Cleveland mentored while Jones was studying at the University of Minnesota.

In the same Eden Prairie building Cleveland bought a few years ago, he helped his son, John, an economist and licensed mechanic, start a garage that repairs hybrid-fuel vehicles. Brad Cleveland was the son of former Riverside Bank CEO David Cleveland, entrepreneur and a founder of the Minnesota Cup.

Brad Cleveland graduated from St. Olaf College and earned a master’s degree in computer science from the University of Minnesota in 1986. He worked as a software engineer for Honeywell and MTS until 2001.

A celebration of Cleveland’s life is planned for 3 p.m. Sept. 27 at the Lafayette Club on Lake Minnetonka.