Erion Shadewhisper is a level 60 rogue trainer located in the Cenarion Enclave in the night elf city of Darnassus. He skulks in the top-secret Rogue HQ that can be found by checking out the area around
[32, 16].
He is likely related to Frahun Shadewhisper.
He starts the quest
[16] Erion's Behest.