Asprin Robert, Heck Peter. Phule Me Twice (In English)

When the planet Zenobia is invaded, Captain Willard Phule is made military advisor. The first priority for Phule's Company: staying out from underfoot of the peaceful, dinosaurlike Zenobians. But unbeknownst to the Zenobians, they're getting two Phules for the price of one as a robot double of Captain Phule appears out of nowhere.