Elizabeth Hoover or better known as Ms. Hoover is a 2nd grade teacher at Springfield Elementary. She is often seen smoking and drinking. Ms. Hoover's students include Lisa Simpson and Ralph Wiggum.
Ms. Hoover was originally voiced by Maggie Roswell from 1989-1999. Roswell then left the show due to a pay dispute.
Ms. Hoover made less appearances since then and small amounts of dialogue.
For these episodes Ms. Hoover was voiced by Marcia Mitzman Gaven.
Eventually Maggie Roswell returned to The Simpsons in 2002, and has been voicing Ms. Hoover and her other characters since then in any episodes they appear in.