You've probably tried this already, but just in case: If you can find a copy of his PhD thesis it's likely (or at least would be likely without the information that you've had trouble tracking down his advisor) to have some mention of his advisor's name in it.
I actually knew about that, but it says "advisor unknown".
Regardless, he certainly knew Tony Hoare, and spoke extremely highly of him.
You've probably tried this already, but just in case: If you can find a copy of his PhD thesis it's likely (or at least would be likely without the information that you've had trouble tracking down his advisor) to have some mention of his advisor's name in it.