Erin Moran, the actress known for her role as Joanie Cunningham in the sitcom "Happy Days," died at age 56 on Saturday. The cause of death was not revealed, but first responders determined the actress was dead after police responded to an emergency call. Moran started her acting career at five years old, and landed her role as Joanie Cunningham at 12 years old. The star continued to act after "Happy Days" ended in 1984, starring in shows such as "Murder, She Wrote" and "Diagnosis Murder."