Dennis ("dmr") Ritchie
Life with Unix says: While he often denies doing as much as Thompson, he is undoubtedly half the reason for UNIX. Largely responsible for C language. For work on UNIX with Thompson, received many prestigious awards including 1982 IEEE Emmanuel Piore award and 1983 ACM Turing Award.
A Research Unix Reader says: Dennis M. Ritchie, best known as the father of C, joined Ken very early on. Dennis contributed basic notions such as fork-exec and set-userid programs. They jointly wrote the fc compiler for Fortran IV. The first debugger db and the definitive ed were Ritchie's, as was the radically new stream basis for IO in v8 and much networking software. With Steve Johnson he made UNIX portable, moving the system to an Interdata machine (v7). The names of Ritchie and Thompson may safely be assumed to be attached to almost everything not otherwise attributed.