Jack Welch, who grew General Electric Co during the 1980s and 1990s into the most valuable public company in the United States, has died at age of 84, the conglomerate said on Monday.

Welch - known as “Neutron Jack” for cutting thousands of jobs - bought and sold scores of businesses, expanding the industrial giant into financial services and consulting.

Under him, GE’s market value grew from $12 billion to $410 billion. But his push to build out the GE Capital financing business nearly proved the undoing of the entire enterprise during the global financial crisis more than a decade ago, and GE now trades at a fraction of its peak value.

President Donald Trump tweeted: “There was no corporate leader like “neutron” Jack. He was my friend and supporter. We made wonderful deals together. He will never be forgotten. My warmest sympathies to his wonderful wife & family!”

In December 1980, it was announced he would succeed CEO Reginald Jones and in April 1981 he took over as the company’s eighth chairman and CEO. He served in that position until he retired in September 2001, succeeded by Jeff Immelt.

GE saw great growth and expansion under Welch’s leadership. Through streamlining operations, acquiring new businesses and ensuring that each business under the GE umbrella was one of the best in its field, the company was able to expand dramatically from 1981 to 2001.

“Before you are a leader, success is all about growing yourself. When you become a leader, success is all about growing others,” Welch wrote in a book called “Winning.”

According to GE’s website, Welch was born in 1935. He received his B.S. degree in chemical engineering from the University of Massachusetts in 1957 and his M.S. and Ph.D. degrees in chemical engineering from the University of Illinois in 1960.

Reuters (Reporting by Rachit Vats in Bengaluru and Nick Zieminski in New York; Editing by Arun Koyyur and Edward Tobin)