The eventual “Glinda the Good Witch” character begins as a young blonde woman, Galinda Upland (of the Upper Uplands), essentially a stuck up aristocrat who is meant to contrast with Elphaba, the young green girl who will eventually become the “Wicked Witch”. The character works to subvert the “good witch” concept by presenting (at least initially) a negative view of Galinda (pretentious, superficial, etc).
Galinda is one of the two main characters in Wicked the Musical (along with Elphaba), and they eventually become best friends after an initial rocky start to their relationship. Both are students at Shiz University, and end up attending Madame Morrible’s sorcery classes. They also are both students of Dr. Dillamond, who is a goat professor.
Dr. Dillamond is the catalyst for Galinda changing her name to Glinda. He has difficulty proncound the “a” sound, a point which initially is annoying to Galinda. However as the story progresses, she removes the “a” in order to show solidarity with Dr. Dillamond and the animals of Oz.