“Larry led us to uncover potential that we never would have seen had he not pushed so hard for increased functionality,” said Vinton G. Cerf, Google’s chief internet evangelist and a graduate student in computer science at the University of California, Los Angeles when Dr. Roberts was overseeing the building of the Arpanet. “He pushed all of us to find ways in which we could make good on the promise of resource sharing.”

He was also a serial entrepreneur and corporate executive. After leaving ARPA in 1973, Dr. Roberts founded or co-founded a half-dozen companies focused on computer networking.

Lawrence Gilman Roberts was born on Dec. 21, 1937, in Westport, Conn., the youngest of three children. His parents, Elliott and Elizabeth, were both chemists who had met in the Yale University chemistry department while pursuing their doctorates.

As a young child, using his father’s chemistry books and chemicals, Dr. Roberts built a series of rockets and bombs. He recalled that one of his youthful experiments produced a chlorine gas byproduct, “which put me in the hospital under an oxygen tent because I sniffed it to see what was happening,” he said in an interview for this obituary in May.

When he was in sixth grade, he built an elevator to ascend an oak tree in his yard. He was sitting in it one day when a connector broke. He fell to the ground and broke his neck. “They were quite used to me in the hospital,” he said.

But it was electronics that eventually captured his attention. “I wanted something new, not old like chemistry,” he said.

He received his bachelor’s degree in electrical engineering from M.I.T. in 1959. That year he married June Stuller, a computer programmer. They divorced in 1974. Three subsequent marriages also ended in divorce.