The Snider Brothers (usually called the Sniders) were two very important players in Dave Arneson's Camapign. In additon to being a Blackmoor player, John M. Snider also ran the Stellar IV campaign for the Blackmoor players which he eventually turned into two science fiction games which were published by TSR - Star Probe (1974) and Star Empires (1977). There were also plans for a third science ficiton game as a sequel to the two previous games. This was to be a roleplaying game that sadly never saw publication.
Richard Snider co-authored Adventures in Fantasy (1979) with Dave Arneson and later went on to create his own roleplaying game, Powers & Perils (1983) with its own unique world. Richard Snider was a member of the predecessor forum to The Comeback Inn until his passing.
Recently, it was discovered that John Snider had taken matters into his own hands. In the 1990s, he ran a campaign referred to as the Egg of Coot campaign. It took place in John's own version of the world of Blackmoor in the lands North West of Blackmoor. John had in fact controlled the Egg of Coot's forces during the early days of Dave Arneson's Blackmoor campaign so who else to expand on this lore if Arneson did not want to do it? Few details about John Snider's Egg of Coot campaign are known, but hopefully more details can still be uncovered. You can read more about it here.