David L. Mills, an internet pioneer who developed and, for decades, implemented the timekeeping protocol used by financial markets, power grids, satellites and billions of computers to make sure they run simultaneously, earning him a reputation as the internet’s “Father Time,” died on Jan. 17 at his home in Newark, Del. He was 85.

His daughter, Leigh Schnitzler, confirmed the death.

Dr. Mills was among the inner circle of computer scientists who in the 1960s through the ’90s developed Arpanet, a relatively small network of linked computers located at academic and research institutions, and then its globe-spanning successor, the internet.

It was challenging enough to develop the hardware and software needed to connect even a small number of computers. But Dr. Mills and his colleagues recognized that they also had to create the protocols necessary to make sure the devices could communicate accurately.

His focus was time. Every machine has its own internal clock, but a network of devices would need to operate simultaneously, down to the fraction of a millisecond. His answer, first implemented in 1985, was the network time protocol.