Dennis Ritchie, 70, Dies, Programming Trailblazer

In the late 1960s and early ’70s, working at Bell Labs, Mr. Ritchie made a pair of lasting contributions to computer science. He was the principal designer of the C programming language and co-developer of the Unix operating system, working closely with Ken Thompson, his longtime Bell Labs collaborator.

The C programming language, a shorthand of words, numbers and punctuation, is still widely used today, and successors like C++ and Java build on the ideas, rules and grammar that Mr. Ritchie designed. The Unix operating system has similarly had a rich and enduring impact. Its free, open-source variant, Linux, powers many of the world’s data centers, like those at Google and Amazon, and its technology serves as the foundation of operating systems, like Apple’s iOS, in consumer computing devices.

“The tools that Dennis built — and their direct descendants — run pretty much everything today,” said Brian Kernighan, a computer scientist at Princeton University who worked with Mr. Ritchie at Bell Labs.