Steve's mother, Doris Pringle. She poisoned Steve as a child and planned to kill him and his father and bury them under the house so they'd stay with her.
The first half of Planes in which Steve inadvertently causes a plane to crash, killing new co-host Linda Barrelli. He finds her charred body in the wreck, and attempts to drive her to the hospital. In the process, he accidentally smashes her against the trunk. This is all shown on screen. With sound effects.