He's a retool of Cybertron Leobreaker, here's the image in question:

It doesn't look like much, but plans were for him to actually have a hand. Unfortunately, costs and engineering difficulties lead to this.
Transforming is easy:
Leo Prime (Starting in robot mode)
- flip down the head
- straighten the arms and legs, and flip up the feet and heels
- remove the underarms, and put then on the bottom of the feet
Optimus Prime (Starting in Super Mode)
- Remove his backpack. Before reconnecting, swing the guns back and up behind the wings.
- fold back one arm as you would for vehicle mode. Usually it's the right
Link Up- Using the plug on Leo Prime, connect him to Optimus' shoulder socket. Make sure the squared pieces of both shoulders are properly alligned.
- Reattach the backpack
Presto.
