Megan Williams is an industrious, sweet-tempered and lovely 10-year-old girl. As designated bearer of the Rainbow of Light, she regularly assists the residents of Ponyland. She is a natural leader - gentle and motherly, resourceful and patient, kind and thoughtful (far more so than most people her age) - which complements her stunning appearance very well. In times of crisis, the Little Ponies often fly across the rainbow to find her. Megan lives with her brother Danny and their sister Molly on a ranch, where they keep a horse named TJ and a bull named Tauro. (The siblings' parents are never seen or mentioned.)
She was first brought to Dream Valley by Firefly, in order to help save her fellow ponies by defeating Tirek. During her quest, Megan encountered the Sea Ponies and the Moochick; the latter gave her a heart-shaped locket which contained the Rainbow of Light. After Tirek's defeat, Firefly brought Megan back home, the girl kept the locket.
She returned once again to help the Ponies defeat the Smooze, bringing along her siblings with her. After that, she and her siblings make regular visits to Ponyland.
In "Rescue From Midnight Castle", Megan wears blue jeans and an orange short-sleeved shirt, with brown boots plus a matching vest and belt. She wears her thick blond hair hair in a ponytail (what else?), which flows down her back and just past her waist, to the seat of her jeans.
- In the My Little Pony Annual 2013 comic story "The Fall of Sunset Shimmer", Megan's name (and also Danny and Molly's) appeared in a flier for the Canterlot High Sundance. She's apparently a teacher who, along with Danny and Molly, handles submissions for the Yearbook in Room E.
- It was thought she appeared in Equestria Girls' Rollercoaster of Friendship but the writers confirmed that it wasn't her.