Trials of Chult
Dead Dwarven Champion
Not sure what the dwarf looks like since you never actually saw him. You know he has a Planer Rune however.
Once a righteous dwarven defender, Zenith disappeared into the Underdark a decade ago.
Upon arriving in Bhal-Hamatugn, the kuo-toan city, the adventurers discovered that rather than being held prisoner, Zenith was instead revered as some sort of prophet.
He was found dead, his withered corpse captured and caged to the tree of Shackled Souls.