Sirius has two strong anchors: it's the brightest star in the night sky (also called the Dog Star, in the constellation Canis Major), and it's Sirius Black, Harry Potter's godfather who transforms into a large black dog. Both references converge perfectly for a dark-coated male dog. At rank 1041, it's a name with genuine depth for owners who want celestial or literary weight, and it has an almost unfair advantage in the astronomy department: the Dog Star naming a dog is almost too perfect.
The Dog Star Angle
Sirius is the brightest star visible from Earth, sitting in Canis Major — the Greater Dog constellation. Ancient Egyptians tracked its rising as a sign of the Nile flood. The fact that it's called the Dog Star makes Sirius one of the few pet names that has an astronomical basis for its use. Owners who know this find it irresistible.
Harry Potter's Long Shadow
Sirius Black was introduced in Prisoner of Azkaban (1999) and became one of the series' most beloved characters. His Animagus form is a large black dog, which means a large black dog named Sirius after Harry Potter is a reference that completes itself visually. It sits in the same literary-pet tradition as Hobbes and Gandalf.
Practical Notes
SEER-ee-us is three syllables that most people shorten to Sirius in one firm beat — SEER-yus. The rhythm works in practice even though it reads long on paper. Breed fit: Black Labs, large dark-coated dogs, anything that looks the part. Compare the celestial register with Orion for another strong option in the same territory.