Life with Unix says: The person to blame for inventing UNIX. For work on UNIX with Dennis, received many prestigious awards including the 1982 IEEE Emmanuel Piore award and the 1983 ACM Turing Award.
A Research Unix Reader says: Ken Thompson began the construction from the ground up based on a file system model worked out with Ritchie and Rudd H. Canaday. He made processors for B, bas, and Fortran besides the operating system proper, and personally installed customized versions of UNIX for early clients as far away as Georgia. With Ritchie, Ken wrote the first shell and piles of utilities including ed, roff, sort, grep, uniq, plot, sa, and dd. He is also known for creative decompiling of mystery code. As if all this weren't enough, he has at the same time written circuit-optimizing tools, switching and network code, C compilers, and the basic software for several special-purpose machines, especially the chess champion, Belle.