Who is Mr. Potts and what does James do for him?

Mr. Potts is a retired farmer. James meets him every day on his pre-lunch walk with Sam. Mr. Potts feels his life is over but lives vicariously through the experiences James shares with him. When Mr. Potts dies, James takes his old dog along on the river walks with him and Sam, his beagle. This cheers up the old dog because he had always joined James and Sam on the walks when his master was alive. His is a service James pays Mr. Potts after his death.