Orion was the son of Neptune. He was a handsome giant and a
mighty hunter. His father gave him the power of wading
through the depths of the sea, or, as others say, of
walking on its surface.

He dwelt as a hunter with Diana (Artemis), with whom he
was a favourite, and it is even said she was about to marry
him. Her brother was highly displeased and often chid her,
but to no purpose. One day, observing Orion wading through
the sea with his head just above the water, Apollo pointed
it out to his sister and maintained that she could not hit
that black thing on the sea. The archer-goddess discharged
a shaft with fatal aim. The waves rolled the dead body of
Orion to the land, and bewailing her fatal error with many
tears, Diana placed him among the stars, where he appears
as a giant, with a girdle, sword, lion's skin, and
club. Sirius, his dog, follows him, and the Pleiads fly
before him.
[ Bulfinch's Mythology, by Thomas Bulfinch ]