Jack Welch, the hard-driving executive who turned General Electric into the world’s most valuable company in two decades at the helm, has died. He was 84.

Under Welch’s leadership, the infrastructure giant’s value multiplied from $12 billion the year he started to $410 billion when he retired, as its revenues spiked nearly fivefold to almost $130 billion in 2000.

But Welch also earned the nickname “Neutron Jack” for his aggressive efforts to slash GE’s workforce. The company reportedly had more than 400,000 employees at the end of 1980, a number that had been cut to about 300,000 just five years later.

A native of Salem, Massachusetts, Welch joined GE as a chemical engineer in 1960 and climbed his way to become chairman and CEO in 1981, a position he held until September 2001.

Welch was known for his intense ire for bureaucracy and an executive prowess that led Fortune magazine to name him “Manager of the Century” in 1999. He streamlined GE’s operations and aggressively acquired new businesses to expand the company’s portfolio.

Among the deals closed in his tenure was GE’s $6.4 billion acquisition of RCA in 1986, which gave it control of the NBC television network. Comcast bought control of NBC from GE in 2011.

Welch retired from GE just days before 9/11 with a roughly $420 million payout and his handpicked successor, Jeff Immelt, taking his place. Welch’s departure left Immelt to wrestle with the fallout from the devastating terrorist attacks as well as the 2008 financial crisis that roiled the company and gutted its financial-services division.

GE’s struggles under Immelt, who left in 2017, clouded Welch’s legacy and caused the firm’s market value to plummet — it most recently stood at roughly $95 billion, less than a quarter of its peak under Welch.

As he watched GE get dismantled, the company’s decline pained him, and he “sometimes said he gave himself an A for his execution of its operations, and an F for his choice of successor,” according to the Wall Street Journal.

“I’m terribly disappointed. I expected so much more,” he said in a December 2017 interview. “I made the best choice I thought I could make and it didn’t turn out right.”

Welch, however, added that he was still hopeful that new leaders would build a “new GE,” the Journal reported.

In retirement, Welch promoted himself as a business consultant and management guru. He wrote how-to books on managing people and competing in a changing world. He gave talks and appeared regularly on his former network, CNBC.

President Trump — whom Welch backed in 2016 before withdrawing his support about a month ahead of that year’s election — tweeted his sympathies for the business titan’s family Monday morning.

“There was no corporate leader like ‘neutron’ Jack,” Trump wrote. “He was my friend and supporter. We made wonderful deals together.”

Welch’s wife, Suzy Welch, announced his death to CNBC on Monday.