Who named canis major the great dog?

The name "Canis Major" for the constellation actually comes from Latin, meaning "greater dog." It's not attributed to a specific person, but rather to the ancient Romans and Greeks who were the first to name the constellations.

They saw the brightest star in the constellation, Sirius, as representing the dog of Orion, the hunter, which is why the constellation was named Canis Major.

It's important to note that many cultures around the world have their own interpretations of the constellation and its stars. For example, the Egyptians saw Sirius as the goddess Sopdet, who brought the Nile's annual floods.