Mr. Wallace

Mr. Charles Wallace was an Elven Sentinel who was sent to Earth to search for the Seven Lords. He disguised himself as an American History teacher and discovered Kat Simonson. He was killed during the Battle of Dolhousie Castle by a Wisp who impersonated him. Kat discovered the Wisp during their journey to White Hall.

Curse of the Spider King
Mr. Wallace discovered Kat was an Elven Lord when he noticed her unusally good score during an American History test. He gave her a copy of The History of Berinfell the next day, and helped get Anna a position as maid at Kat's house. He traveled with Kat and Anna to Scotland. At Dolhousie, he formed the rear guard heading for the portal and was killed by a Wisp.

As a Wisp: End of Curse of the Spider King, Venom and Song
He stabbed Mr. Charlie after the later's battle with Mobius and snaked through the portal in his smoky form. He traveled with the party to Nightwish Caverns and was mainly why the Elves' stronghold was discovered. He overturned the boat he was in on Daladge Falls. He voted for the journey to Whitehall, and allerted a party of Gwar and Warspiders along the way, hoping one of the Seven would die. When they escaped down a zip-line, he rode in the same harness as Kat, and attempted to kill her. She stabbed him and he dropped his weapon and turned into smoke.

It is implied later in the book that the same Wisp who impersonated Mr. Wallace impersonated Kiri Lee, though it is not know if Wisps actually have distinct personalities.