The name
I'd change the name since "Ryuk" isn't really a name and is pretty much unique to Death Note. If you want it to sound Japanese or something, you should put some hiragana/katakana together and pronounce it like that (you can't end something with just "k" in Japanese). Anyhow, it's an original character, so you should make an original name, too.
As for the picture itself, it's pretty good. Those lines/muscles on the neck don't make much sense, though. From what I know, they go from behind your ears down to the middle of your collar bone. The lines on the inside are doing that alright, but the one more to the right sure isn't. I don't think the muscle should be that defined when this character is relaxing like this, though; I'd personally only show one set of lines, not both.
The raised arm looks like it's too close to the body; the angle you have it on might even be impossible, but I'm not entirely sure.
The hand, hair, and face look very good, though the mouth looks a little off center. The colouring is quite nice.