Dennis Ritchie

Dennis MacAlistair Ritchie (September 9, 1941 – c. October 12, 2011) was an American computer scientist. Along with his longtime collaborator Ken Thompson, he developed the Unix operating system, the C programming language, and the B programming language.

Born in Bronxville, New York, Ritchie was the son of Alistair E. Ritchie, a Bell Labs scientist who co-wrote *The Design of Switching Circuits*. The family later moved to Summit, New Jersey, where Ritchie graduated from Summit High School. He earned degrees in physics and applied mathematics from Harvard University in 1963.

Ritchie joined Bell Labs’ Computing Science Research Center in 1967. The following year, he completed a draft of his Harvard PhD thesis, “Computational Complexity and Program Structure,” supervised by Patrick C. Fischer, but never officially received the degree. (A copy of the lost dissertation was later found in 2020 by the Computer History Museum, working with both families.) In the 1960s, Ritchie and Thompson worked on the Multics operating system at Bell Labs. Thompson then found an old PDP-7 machine and, with help from Ritchie and others, built his own operating system and applications from scratch. In 1970, Brian Kernighan coined the name “Unix” as a pun on “Multics.” To replace assembly language with a system-level language, Thompson created B, which Ritchie later replaced with C. Ritchie continued refining Unix and C for many years.

During the 1970s, Ritchie collaborated with James Reeds and Robert Morris on a ciphertext-only attack against the M-209 US cipher machine, effective on messages of at least 2000–2500 letters. After discussions with the National Security Agency, the authors chose not to publish, as the technique applied to machines still used by foreign governments. Ritchie also contributed to the Plan 9 and Inferno operating systems and the Limbo programming language. Following an AT&T restructuring in the mid-1990s, he moved to Lucent Technologies, retiring in 2007 as head of the System Software Research Department.

Ritchie created C and was a key developer of Unix. With Brian Kernighan, he co-wrote *The C Programming Language*, often called K&R. He worked closely with Thompson, who wrote the original Unix; Ritchie’s contributions included porting Unix to different machines and platforms. Doug McIlroy later noted that “the names of Ritchie and Thompson may safely be assumed to be attached to almost everything not otherwise attributed.” C is widely used in applications, operating systems, and embedded systems, and its influence appears in most modern programming languages. It is a low-level language with constructs that map closely to hardware instructions, yet it is not tied to any specific hardware, making it portable. C also serves as a high-level language with constructs for application data structures. It influenced languages like C++, Objective-C (used by Apple), C# (Microsoft), and Java (used in corporate environments and Android). Ritchie and Thompson used C to write Unix, which established many computing concepts still widely adopted.

In a 1999 interview, Ritchie described Linux and BSD as continuations of Unix’s foundation, calling Linux “quite delightful” for drawing strongly on Unix. He added that he viewed Unix and Linux as “the continuation of ideas that were started by Ken and me and many others, many years ago.”

Ritchie and Thompson received the 1983 Turing Award for their development of generic operating systems theory and the implementation of Unix. Ritchie’s lecture was titled “Reflections on Software Research.” In 1990, they received the IEEE Richard W. Hamming Medal for originating Unix and C. In 1997, both were named Fellows of the Computer History Museum for co-creating Unix and developing C. On April 21, 1999, President Bill Clinton awarded them the National Medal of Technology for 1998, citing their work’s role in advancing computer hardware, software, and networking, and stimulating an entire industry. In 2005, the Industrial Research Institute gave Ritchie its Achievement Award for his contributions to science and society through Unix. In 2011, Ritchie and Thompson shared the Japan Prize for Information and Communications for their Unix work.