While the group of players has already met Fillyar Buck so I can upload this image of him there isn’t so much that I can tell about him without writing any spoilers for the players in the group. What they already learned is that Fillyar Buck was a representative of the ponys of Trottingham during the peace negotiations that led to the treaty of Trottingham after the last battle between ponys and griffons 27 years before the time in which our role play game adventure is set.
After signing the treaty Fillyar Buck left the Griffish Isles for some years since he had requested to serve Princess Luna who granted this request. For several years he was part of what one might think of as the entourage of Princess Luna (all of this is before her fall and turn to Nightmare Moon) before he finally asked to be dismissed for missing his home on the Griffish Isles (a request which Princess Luna regretted but granted).
After returning to the Griffish Isles he again became an important voice in the town council. He also became the main teacher for the kids in Trottingham and the archivist of the town.
There is an alternative version of the above drawing with reduced opacity to let the parchment background shine through.