He is known for his strong leadership and courage and would easily sacrifice himself for the safety of others. His selfless personality is one of many traits that made him a great leader. Optimus Prime could be easily described as a "reluctant warrior", in that he only engages in war when absolutely necessary. It is possible this attitude prolonged the Autobot/Decepticon war.
He and Megatron (or his numerous iterations) have always shared a mutual respect for each other, and have opposed each other in nearly every depiction of the Transformers universe.
In the 1986 Transformers animated film, Optimus Prime was killed after a fierce battle with Megatron, but his character returned several times during the series.
Optimus Prime was the most liked character among young viewers of the original series, although his toy was not the highest selling (original release, excludes all others).
Megatron: "Why throw away your life so recklessly?"
Optimus Prime: That's a question you should ask yourself, Megatron.."