Tim Kirk (SF encyclopedia link; his website is defunct and his wikipedia page is an error-riddled paraphrasing of this entry as far as i can tell)

it took me a minute to find the actual artist because this fellow's folder was saved as tom kirk - and, in tribute to how much of the internet is junk copy-pasted from junk, there is A summary of the book a tolkein treasury floating around that calls him "tom" that's popped up in listings of the book for sale. (even though his name is on the back... it's tim...) it's weird how a typo can get stuck in the content mill like that.