Old Tom is probably the best answer....
But, who else would be eligible?
Ross had various people (my home course is a Ross but there is documentation that he wasn't really there)
Tillinghast had people, as he was building multiple course concurrently?
Macdonald had Raynor/Banks
Allson had Colt and even McKenzie (at one point)
McKenzie had someone? Or did he?
Jones, Nicklaus, Dye, Fazio, Hills, Palmer, et al are all out of the question
Did Fowler have anybody with him?
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Strantz (as a singlehanded builder/designer) or Keith Foster (as a single-handed designer)