Cyparissus was a mortal boy, teen, or man depending on the version of the story, who was a lover of the greek God Apollo.  He had a pet deer, whom he adored more than anything else in the world.  One day, while in the forest, Cyparissus accidentally discharged his bow, mortally wounding his pet.  Consumed with grief, remorse, and guilt, he threw his body over the suffering companion as the pet died, transforming into what we now call the Cypress tree.