If you type 'greatest golf player ever' in a search engine you will find a number of top 10 lists based on different criteria. The most carefully chosen lists are usually based on players' performance in the major world championships including the Masters and US Open. Names that come up all the time - in this list, for example - include Jack Niklaus, Gary Player and Tiger Woods. Some vote Tiger Woods as the best player ever. Tom Watson and Arnold Palmer usually feature in the top 10, but not the top 5.
So there is clearly not a single definite answer, but the name that features most consistently at the top of such tables is Jack Niklaus.
The winner of 18 top championships, the 'Golden Bear' as he is often called, is now almost 73 years old but was still playing professionally -at least part time - until a few years ago. He has also written some of the world's most popular golf instruction materials.