Maude Flanders was the wife of Ned Flanders and mother of Rodd and Todd and like all members of her family she was a Christian. Maude had very strong beliefs and would often partner with Helen Lovejoy in protest against the "evils" that plagued Springfield.
Maude Flanders unfortunately died in a tragic accident but she has made some further appearances on the show in alternate futures, visions and flashbacks.
Maude Flanders was originally voiced by Maggie Roswell from 1989-1999. Roswell then left the show due to a pay dispute.
Maude Flanders was featured in less episodes since then and when she did have some dialogue it was very short.
For these episodes Maude Flanders was voiced by Marcia Mitzman Gaven.
Eventually Maggie Roswell returned to The Simpsons in 2002, and has been voicing Maude Flanders since then in any episodes the character appears in.