It's a tomato hornworm. The are so effective in camouflaging themselves among the tomato plants. You literally can't see them. Once you've seen one then you can see others. Last year I have several dozens of these pests and since I try to be as organic as possible they won the battle. I still got a good crop of tomatoes though. This year I will be moving my tomatoes to a different location in the garden and if they do come back I will ask to neighbor kids to come over and pluck them and give them to their chickens! I have a real problem squashing a 4 inch meaty little worm. Though I will say they are very photogenic. It's amazing what you will see in the garden once you really start looking.