Complex sentence: "The Three Kings" refer to the three brightest stars of the Orion constellation, called ζ Ori (Alnitak), ε Ori (Alnilam), and δ Ori (Mintaka).
Split into simpler sentences: The Three Kings refer to three of the brightest stars in the Orion constellation. These entities are known as ζ Ori (Alnitak), ε Ori (Alnilam), and δ Ori (Mintaka).