Richard Guy passed away on March 9, 2020 at the age of 103. Before he died he was the worlds oldest living mathematician (see here for a list of centenarians who are famous scientists or mathematicians). He was also the oldest active mathematician-- he had a paper on arxiv (see here) in October of 2019. (ADDED later since a commenter pointed it out to me--- a paper by Berlekamp and Guy posted in 2020: here)
I met him twice- once at a Gathering for Gardner, and once at an AMS meeting. I told him that Berlekamp-Conway-Guy had a great influence on me. He asked if it was a positive or negative influence. He also seemed to like my talk on The Muffin Problem, though he might have been being polite.
I did a blog about Richard Guy on his 103rd birthday, so I recommend readers to go there
for more about him. One point I want to re-iterate:
Richard Guy thought of himself of an amateur mathematician. If he means someone who does it for love of the subject then this is clearly true. If it is a measure of how good he is (the term `amateur' is sometimes used as an insult) then it is clearly false. If it means someone who does not have formal training than it is partially true.