Who's This? Don't be fooled by the Irish name, he's dressed as a djinn or something on page 10 of Who's Who Update '87 #3.
How you could have heard of him: The 1999 JSA series made use of him in early issues, having played a part in Alan Scott's son having shadow powers and becoming Obsidian. His last name was used for a Lovecraftian entity in a Superman: The Animated Series episode that co-starred Dr. Fate.
Example story: More Fun Comics #69 (1941) by Gardner Fox and Howard Sherman
Who's Next? A lame Batman villain that didn't make it in the first volume of Who's Who!