+1 to ocdecio - if he is a star developer, then his code should be based on such a high-quality design that it documents itself.
Having said that, the frustration could be that although he's excellent in technically-demanding areas which are interesting to him, he doesn't muck-in with the delivery of features - only you will know whether this is a problem for your organisation.
Having a "guru" available can be an absolute life-saver - or at least it used to be, or has StackOverflow made that role redundant?
