Ritchie began working at Bell Labs in 1967; Ken Thompson, who is known as the other half of the team that developed UNIX, had joined a year earlier. The pair originally developed UNIX in 1969.
Others like Brian Kernighan, Douglas McIlroy, and Joe Ossanna also contributed to the system that served as the inspiration for a later generation of programmers like BSD pioneers Bill Joy and Marshall McKusick and Linux creator Linus Torvalds.
UNIX came about because the operating system that AT&T Bell Labs, along with MIT and GE, had developed in the 1960s, Multics, had many problems despite introducing a number of innovations. A small group decided to redo things on a much smaller scale.
Ritchie is also known for having co-authored the book on C, The C Programming Language, along with Kernighan.
His achievements earned him the Turing Award in 1983. He was also awarded the US National Medal of Technology for 1998.
He was head of Lucent Technologies System Software Research Department when he retired in 2007.
"His development of the C programming language an co-development of UNIX from 40 years ago are the foundations of any serious computing that is conducted today. It is extraordinary to find longevity of that nature in computer science. The latest and most popular UNIX-like operating system, Linux, owes so much to this great individual.
"Perhaps the best way that Linux developers could give recognition would be to integrate the features that Ritchie was working on in Plan9, such as representation of remote system resources as files, and namespace hierarchy to be process group specific rather than system based. It would be nice to get a bit more of his spirit into the project."
Lafayette, a doctoral candidate at the Ashworth Centre for Social Theory and an experienced ICT generalist, specialising in the Linux operating system and networking technologies, said that like many other people his introduction to Ritchie's work was the famous book on C.
"That was a long time ago - I remember at first finding pointers to be challenging but once they were understood it was a challenge not to use them for everything!" he said.
"Rereading this classic text is fascinating. It's like walking through a old house and looking at the richly detailed classic furnishings. Best still, there's still hauntings there.
"I have enormous admiration and respect for the work of Dennis Ritchie, and my condolences to his friends, family and colleagues. The world has lost a great mind and a humble person with his passing. We will do our best to honour the work he has done."
Jenkin, a freelance UNIX consultant based in Canberra and one of those behind the institution of the John Lions Chair in Operating Systems 2006, added: "The most important derivatives of his language are Objective-C, used by Apple to write their OS/X and iOS systems and Java, used extensively by IBM and Oracle. Losing Dennis is a very sad loss."
Greg "Groggy" Lehey, a prominent member of the BSD community and a veteran hacker, expressed his admiration this way: "If ever there was a 'giant', it was Dennis. I can't think of any part of modern computing environment which he hasn't influenced."
Lehey, who is a developer with both the NetBSD and FreeBSD projects, added: "Most modern compiled programming languages are either his own C programming language, or they're derived from it. His file system design is alive and well today and forms the basis of almost all modern file systems with the exception of Microsoft.
"Everybody who uses a web browser (in other words, everybody) sees the file name conventions that he developed 40 years ago. And as one of the two main developers of UNIX, he has influenced all operating systems, even to some extent Microsoft. There's not a single product that Steve Jobs marketed in the last 20 years that doesn't depend on Dennis' work."