I don't think Carter had any input. There was some (minimal) input from Zapf, mostly with respect to the calligraphic capitals. Mostly, Knuth was trying to repl

I don't think Carter had any input. There was some (minimal) input from Zapf, mostly with respect to the calligraphic capitals. Mostly, Knuth was trying to replicate the Monotype Modern. Some of the fonts like cmr17 are especially bad (the extrapolation of parameters to larger design sizes was not correct). That said, I do think that cmtt is a superior typeface for monospace typesetting.