Cassin's kingbird is a large tyrant flycatcher native to western North America. The name of this bird commemorates the American ornithologist John Cassin.

The tyrant flycatchers (Tyrannidae) are a family of passerine birds which occur throughout North and South America. They are considered the largest family of birds known to exist in the world, with more than 400 species. They are the most diverse avian family in every country in the Americas, except for the United States and Canada. The members vary greatly in shape, patterns, size and colors. Some tyrant flycatchers may superficially resemble the Old World flycatchers, which they are named after but are not closely related to. They are members of suborder Tyranni (suboscines), which do not have the sophisticated vocal capabilities of most other songbirds.