Thats Godzilla, (Pholidichthys leucotaenia) he's an engineer goby or convict blenny depending on which name the LFS puts on it.
Extremely hardy SW fish, probably the hardiest fish you can get for SW. Also very non-aggressive towards other fish. (looks mean though doesn't he?)
i currently have 2 enginer's in my 125. at first i was worried about a rock slide, but i repositioned the rocks. and am greatly pleased that i did not take them out. your rite, they are very peace full, but look bad