Tildanyorion is a High Elf warrior and member of the Undaunted who can be encountered in the Undaunted Enclave in Mournhold. He's inside the pavilion leaning up against the Echatere cage. He has no unique dialogue.
It is very difficult to pickpocket him due to his position. To do so, crouch between the Khajiit guardian statue and the empty cage, and zoom your camera view really far out in third person, pointing your crosshair at the echatere.