He (as I understand it, though, perhaps I am wrong about this) essentially invented the field (Friendly Artificial General Intelligence) as an area for substantial study and set out some basic research programs. The main one of which seems to be a decision theory for an agent in a general environment that is capable of overcoming the issues that current decision theories have; mainly that they do not always give the action that we would recognize as having the greatest utility relative to our utility function.
Well, here are my two cents. (1) It isn’t strictly correct to call him an AI researcher. A more correct classification would be something like AGI theorist; more accurate still would be FAI theorist. (2) Normal anomaly mentioned his TDT stuff, but of course that is only one of his papers. Will Newsome mentioned CFAI. I would add to that list the Knowability of FAI paper, his paper coauthored with Nick Bostrom, Coherent Extrapolated Volition, Artificial Intelligence as a Positive and Negative Factor in Global Risk, and LOGAI.
He (as I understand it, though, perhaps I am wrong about this) essentially invented the field (Friendly Artificial General Intelligence) as an area for substantial study and set out some basic research programs. The main one of which seems to be a decision theory for an agent in a general environment that is capable of overcoming the issues that current decision theories have; mainly that they do not always give the action that we would recognize as having the greatest utility relative to our utility function.