Who is un Owen in and then there was none?

Justice Wargrave. He was the only one who actually didn't commit a murder. Seton was guilty.

U.N. Owen is also the name related to Flandre Scarlet from the 3rd-person shooter Touhou game series. Her theme is titled "U.N. Owen was her?" (Title based off Agatha Christie's novel "And Then There Were None") and because of it's upbeat, catchy nature, it has developed into an internet meme in it's own accord.