He LOVES Transformers. The original and the more young kid-friendly Rescue Bots. He is constantly drawing and playing with his various Optimus Prime toys.
(And of course requested to be Optimus for Halloween.)
He also thoroughly enjoys Legos. So why not combine his two loves?
He is very specific on how they transform. If you do it wrong he will let you know. Below is an example:
And here is guy mode.
Suffice to say, if Eli turns out to be a car designer, we will have the best vehicles in town.