In Transformers, the Autobot leader who turns into a red-and-blue truck is Optimus Prime.
Optimus Prime is the leader of the Autobots, a faction of sentient mechanical beings from the planet Cybertron. In the 2007 live-action film directed by Michael Bay, he arrives on Earth while searching for the AllSpark and opposing the Decepticon leader Megatron. His vehicle mode is a red-and-blue Peterbilt 379 truck.
Optimus is voiced by Peter Cullen, who also voiced the character in the original 1980s animated Transformers series and The Transformers: The Movie. The live-action version retains his recognizable blue helmet, faceplate, leadership role, and commitment to protecting humans and other Autobots.
The term “Transformer” describes the species and their ability to change form, not a separate robot model. Bumblebee is another famous Autobot, but he is a scout and changes into a car rather than the truck associated with Optimus. Megatron is Optimus’s principal Decepticon rival and does not lead the Autobots.