I don't have a photo of Tom, so this sketch will just have to do:
That's the first sketch I drew of Tom, and is pretty conservative. A careful, reserved study of the basic shapes that form his face. And overall head shape.
In addition to striving for a likeness, I like to include something more about the person I'm caricaturing. Tom's a painter, so my first attempt at this was to stick his head on the end of a paint brush.
I tried to simplify things a bit in my next sketch, which involved an even closer look at what was going on in Tom's face that made him uniquely him. I then played with that a bit:
I couldn't help adding some whiskers. Don't ask me why. I suppose it's the size of his nose, the shape of the tip along with the shape of his mouth as well as the facial hair that suggested a small rodent-ish look to me.
In my final sketch I built on everything I'd observed so far:
I think the design works as a cartoon character yet still retains a lot of the qualities I look for in caricature.