She originated pretty much every female character on South Park. She provided the 3 primary voices for this Oscar-nominated song.
Her voice talent graced most of the major animated works of the 90s, from Rugrats to The Tick to Family Guy, including 3 Disney features. 4 if you count the yodeling they kept for Toy Story 2 (Joan Cusack rerecorded role of Jessie, but they kept her yodeling). Hey look, someone did a montage!
She took her own life in 1999 after struggling with mental illness; she was 38. The Mary Kay Bergman Memorial Fund contributes to a suicide prevention service.
Her gravestone is actually pretty cool.
Happy birthday dude. Rest in peace.