Hello, I'm applying for my phd in field X at the moment. Two years ago I did a 2-month research project on X under guidance of one of the leading figures of that field (Prof Y). Now, he is notoriously hard to get a hold of (even his phd students struggle) and he isn't responding to any of my requests for a reference letter (including calling his secretary who was supposedly going to give him a note). I know this sounds as if I did bad work and that's why he isn't giving any response, but really my research with him went well (he told me that himself afterwards) and as I said most people I know have a problem with getting hold of him (last year I managed to get a letter from him after finally being able to get hold of him). So I'm thinking of giving up and asking another referee (who would probably write an ok/good letter; also I already have two good letters in the bank). I'm not worried about not getting a letter from a famous researcher (I wish that were it), what worries me: they will see I have done research with Prof Y (it would be foolish to leave out that experience in my Statement), and they will certainly know of him, so if I don't have a letter by him, I worry that they will conclude it was a bad experience? Or will they not assume that if my other letters (some research related) are good? Thank you!