In the first series his alternate mode is a red, silver and blue Kenworth K100 cab over truck.
Before becoming leader of the Autobots, Optimus used to be a smaller robot called Orion Pax. He was mortally damaged by Megatron, but Alpha Trion reconstructed him into the ultimate powerful form of Optimus Prime.
In Japan (except for the Japanese dubs of the live-action films and of Transformers Animated), Optimus Prime is known as Convoy.
His quote in the G1 series, ”I've got an idea.” is regarded as a type of meme among Japanese Transformers fandom due to its low success rate.
Optimus Prime's original G1 design was created by mecha designers Obara Hiroyuki, Kawamori Shouji (famous for his work in Macross) and Ohno Kouhjin for the Diaclone japanese transforming robot toy series in the early 80s.
Motto: "Freedom is the right of all sentient beings...".