This is the nice farmer who finds Lone injured in the woods after the beating from Mr. Kew.
Mr. Prodd takes Lone in and, along with his wife Mrs. Prodd, begins healing him. While Mrs. Prodd sings to Lone and bakes him a birthday cake, Mr. Prodd works with him out on the farm. Kind of a Steinbeck vibe going on there.
The farmer also hears Lone struggling to assert "All alone" as his name and interprets the vocalizations as meaning "Lone" (1.11.10). So Mr. Prodd partially helps Lone name himself, just as Lone's stay with the Prodds is only a partial success (unlike the gestalt belonging). The Prodds really just see him as a substitute for their fantasy son Jack.
Once Lone figures out that he's a mere substitute, he takes off to the woods, but returns to Mr. Prodd's farm to borrow an ax. Mr. Prodd asks Lone kind questions, but realizes "He's a good boy but not the kind to set around and visit" (1.22.20).
Mr. Prodd's truck gets stuck, which causes Lone to return with—of all things—an anti-gravity generator to help. But Mr. Prodd has gone mad, as Lone finds out from a partial probe of his mind. He goes mad because Mrs. Prodd gave birth to Baby and not to Jack. He leaves a note for Lone that he's gone to Williamsport, Pennsylvania to look for her, not realizing, as Lone does, that she died in childbirth. Mr. Prodd ends up in a Pennsylvania insane asylum.
That's where he meets Hip and tells him that Lone lived in the woods with the animals, and that he, Prodd, had never missed a milking. Hip thinks of him as "the happiest human being" he's ever seen (3.12.11). Well, all's well that ends well, we guess.
We also think it's cute that he courted Mrs. Prodd in "his boss's Model T and [...] not even knowing how to drive it yet" (1.9.23).
Mr. Prodd's role is to heal Lone and provide him with a partial sense of belonging that's basically a halfway point between the sheer loneliness he feels at the start of the book and the full sense of belonging he has with the gestalt. Though he fails to provide perfect belonging for Lone, Mr. Prodd is essentially a good guy, as his ultimate fate as a happy asylum resident seems to suggest.
One last note—think about his name. He prods Lone's evolution!