The Good Witch who appears at the start of the 1939 film is Glinda.
After Dorothy’s house lands in Oz, Glinda appears in a bubble and introduces herself as the Good Witch of the North. She explains that Dorothy’s arrival has killed the Wicked Witch of the East and that the witch’s enchanted slippers now belong to Dorothy.
Glinda is played by Billie Burke, whose elegant costume and calm manner helped define the character for generations of viewers. In L. Frank Baum’s 1900 novel, Glinda is the Good Witch of the South, but the film changes her title to the Good Witch of the North.
A common mix-up is confusing Glinda with Addaperle or Locasta, names associated with other Oz adaptations and stage versions. The 1939 MGM film’s opening Good Witch is unambiguously Glinda.