I’ve read somewhere that Dan Khanna is the most famous or greatest fan artist of Transformers from the 1990s. I’m not going to vouch for that claim since I’ve really only heard of the guy this year. I know he’s pencilling some work liscensed by Hasbro so he’s not really a fan artist so much as he a professional artist. Either way, a large repository of his stuff can be found on a UK site here.