Fineous Darkvire, chief architect of the Dark Iron Dwarves, can be found within Blackrock Depths.
While not a particularly special boss, he drops an uncommon quality purple shirt which doesn’t show up anywhere on his loot table. Due to the drop being unmarked in-game, the shirt has remained relatively unknown despite having been in the game since Vanilla.
Fortunately, this shirt is easy to farm. It has a 7% drop chance, and you can kill Fineous and reset the dungeon in the span of a few minutes. The fastest way to farm the Master Builder’s Shirt is to take the mole machine at the start of the dungeon to “Just pas the Grim Guzzler“, jump off the ledge, and kill Fineous. Then run back outside, reset the dungeon, and do it again.
Statistically, you should get the shirt within 15 runs, but if it takes a few more don’t get discouraged! Just stick with it and pretty soon you’ll be walking definition of fashion with an awesome new shirt.