The Thunderbird is a form that Grandmother occasionally takes.
The Thunderbird is an enormous, formidable bird, with a second face in its stomach. Grandmother shape-shifted into the Thunderbird during Goliath and his companions’ visit to Queen Florence Island in the hopes of using that form to convince Natsilane that creatures of myth exist. Goliath and Angela fought her after they mistook her intentions thanks to Raven's lies. ("Heritage")
- "Heritage" (First Appearance, No Lines)
Real World Background
The Thunderbird appears in Native American mythology as a bird of prodigious size and power, more a spiritual being than a mere bird. Despite its great size and strength, it is benevolent, does not harm or kill anyone, and has often blessed humans; for example, it taught the Kwakiutl how to build houses. This ties in rather nicely with its being an alias of Grandmother in the animated series.
- Thunderbird at Wikipedia, the Free Encyclopedia