I was doing some research on Wikipedia yesterday and came across the entry for Thanatos, which mentions his twin brother, Hypnos. Throughout the article, and the sources, including Homer, they are referred to as twins. However, the article also contains reference to the John William Waterhouse painting “Sleep and His Half-Brother Death.”
From what I’ve read, Waterhouse created his painting after his younger brothers died. I just can’t find any reason it’s titled “Half-Brother.” Maybe his younger brothers half-brothers, or is this an example of weird Greek God genealogy where they actually did have two different dads?
Thanks for your help 
Well, Thanatos and Hypnos are from Greek mythology and supposedly Nyx is their Mommy and Erebus is their Daddy so they are full brothers and in fact are described as twins. So I can think of a couple of explanations. Maybe the artist made a boo-boo. More likely, he was just imagining his own fictional universe with Sleep and Death, while based on Greek mythology, being his own characters with their own back story.
Continuity in story-telling didn’t really become a big thing/requirement until the internet and freeze frame.
Maybe Waterhouse’s own spin, maybe there are versions of the Greek myths where they don’t have the same dad.
It seems to me that the title refers not to the relationship between the people, but to the relationship between the states of sleep and death.
That is, sleep is the half-brother of death, because they share certain superficial characteristics (stillness; the appearance of unconsciousness; etc.), but are not the same.
It is possible, even in the human world, for twins to be half brothers: Is it possible for fraternal twins to have different fathers? - The Straight Dope Much stranger things than that happened with gods.
It’s also pretty common in Greek mythology for parentage to vary from story to story. However, they’re pretty consistent about Nyx being the mother of both Hypnos and Thanatos. Fewer stories mention Erebus as their father, but I can’t find any that say it was anyone else. Of course, gods didn’t always need two parents. Would Artemis (born of Zeus and Leto) be a full or half sister of Athena (often said to be born of Zeus alone)? If Hypnos and Thanatos were both parthenogenetic, what would that make them?
