Guy L. Steele - no proper language design can go without him. I think he is the only person who enjoys writing language reference manuals and is able to explain every language detail mathematically and linguistically everyone can understand. He was behind C, Java, Scheme, Common Lisp, ECMA, Fortan...
Perhaps you mean behind standards and reference manuals for, rather than behind the languages? Behind Scheme and Common Lisp, okay. But he contributed to standardisation and documentation of the others after their creation, rather than being one of their designers.
Incidentally, Steele has an anecdote of perhaps an early instance of pair-programming with someone else mentioned in these HN comments, Richard Stallman (at the end of this chapter): https://www.oreilly.com/openbook/freedom/ch06.html
