When TA first began, Dan Archer was the good farmer and Walter Gabriel was the bad farmer (a role taken by Joe and Eddie Grundy in later years). This made it possible for the Ministry of Agriculture to get its propaganda across by having Dan explain to Walter where he was going wrong whenever the warble fly struck or the pigs didn't fatten up to plan.
However, because it was also a soap, they decided to give Walter a ne'er-do-well son who was suspected of involvement in a Borsetshire version of the Great Train Robbery, thus causing Walter a great deal of heartache. Nelson disappeared for a while, I think (this was long before I was listening but I am another saddo enthusiast with lots of Archers books). Later, he came back to Ambridge and opened a wine bar in Borchester which was where all the yuppies hung out in the 80s (this included Shula, Mark, Caroline, Nigel, Tim Beauchamp and, later, Lizzie).
Nelson was an utterly wonderful character, because having cast Jack May for the part, the production team wisely decided to let him use his own gorgeous voice rather than trying to get him to do a junior version of Walter's Mummerset accent. Thus Nelson sounded like a member of the Royal Family, which was rather odd given his roots as a member of the Ambridge working classes, but hey! he was so witty and urbane, who cared about plausibility?
There was a suggestion that Nelson swung both ways but he was very fond indeed of Nigel's mother, Julia, and they became good friends. He also turned out to have a long-lost daughter, Rosemary, who was a police officer, rather to his chagrin.
Eventually he left Ambridge in mysterious circumstances and was later reported to have died in South America. There was an odd incident when people were spotted digging up the garden of Honeysuckle Cottage which had been his home (Adam and Ian live there now). This may have been to find the loot from the train robbery.
Happy days.