Hans and Sybil Eysenck
In 1976, I wrote to Hans Eysenck with some comments on his trilogy of Pelican books, raising (what seemed to me to be) some problems with some of his contentions and making some suggestions. In reply, I expected to get at most, in due course, a brief note thanking me for my comments.
Instead, I got by return post a letter replying in detail to every point I had raised.
From that time on I corresponded casually with Professor Eysenck until near the time of his final illness, always receiving -- busy though he must have been -- prompt, courteous and detailed replies, and (once) even advance copies of his research papers!
And so, although we only ever met one time, I shall always remember him, not only as a brilliant researcher and writer, but a kind and generous gentleman.