This comic book character looks eerily like The Master of Darkness*. His appearance in "Kingdom Come", the DC Comics graphic novel by Mark Waid and Alex Ross**, led some (including the Webmistress) to believe it was really an unacknowledged appearance by The Shadow. In fact, Obsidian is a separate character.
Obsidian is the son of the original Green Lantern (Alan Scott) and the brother of Jade. He can merge with his shadow, and controls a "dark shadow force". Obsidian is part of "Infinity Inc."***, which was introduced in the comic book "All Star Squadron" (issue #25) in the 1980s. Recently, he has appeared more as a villian than a good guy. (Thank you to Phillip Grant for the information!)
For more information about this character:
The Unofficial Infinity Inc. Web Site
Obsidian in "Kingdom Come"
* He has a much different appearance in other comics than in "Kingdom Come". Visit the link above for a picture.
** "Kingdom Come" featured all the DC Comics superheroes and their descendants.
*** Infinity Inc. was an off-shoot of the Justice Society of America (another DC Comics series). Founding members included Silver Scarab, Fury, Nuklon, Jade, Northwind, Star-Spangled Kid and Power Girl. Brainwave joined later.