Read from the World of Warcraft client build files (JournalEncounterItem, JournalEncounterCreature, Achievement) and the Blizzard Game Data quest API.
How Gleamkeeper's Buckle Compares
Who It Suits
Leather is the armor type Demon Hunter, Druid, Monk and Rogue wear. With Agility or Intellect, Gleamkeeper's Buckle suits Assassination, Outlaw and Subtlety Rogue; Brewmaster, Mistweaver and Windwalker Monk; Balance, Feral, Guardian and Restoration Druid; Havoc, Vengeance and Devourer Demon Hunter.
Transmog Sets
Gleamkeeper's Buckle is part of the transmog set Coreway Regalia (Rogue, Monk, Druid and Demon Hunter only). The other 16 pieces:
Blizzard numbers items as they are created, so the named items next to ID 221107 (221102 to 221112) were usually added in the same batch as Gleamkeeper's Buckle: the same quest line, zone, vendor or reward set.