"[...] Knuth definitely wrote most of the code himself, at least for
the Metafont re-write, for which I have pesonal knowledge. However,
some of his students (such as Michael Plass and John Hobby) did work
on the algorithms used in TeX and Metafont. He also did have a
programmer (David something) working for him at one point, but not
as I recall at the time of the Metafont re-write."
That said, some solid source on the earliest phases, as well as on particulars of the specific "algorithms", would be nice to learn.
