First ran across the keyboard probably 5+ years ago and have been mentally pronouncing it “EH-tree-us” (that’s “eh” in the Canadian fashion), but was talking with a friend who said “uh-TRAY-us”, which (in addition to reminding me of that character from The Neverending Story ) made me notice that I’ve only ever seen the name written down. (And also that I don’t know the name’s origins, but I find it’s safe to assume “Greek mythology” for things named by programmers )
Atreus was the father of Agamemnon & Menelaus (mentioned in the Iliad). Emphasis usually placed on the first syllable, with a long A sound like in the word “bake”. How the subsequent vowel sounds are pronounced varies more. Atreus - Wikipedia
) made me notice that I’ve only ever seen the name written down. (And also that I don’t know the name’s origins, but I find it’s safe to assume “Greek mythology” for things named by programmers 
)