Optimus Primal was a
Maximal who took his name from the great
Autobot leader
Optimus Prime. Originally the commander of a science vessel, he and his crew were sent to capture and return
Predacon criminal
Megatron to
Cybertron to stand trial for stealing the
Golden Disk.
The chase led them to prehistoric Earth via Trans-warp drive. According to Beast Wars prehistoric earth was seeded with unstable energon crystals by an alien race known as the Vok. To protect themselves, the transformers used DNA scanners to create alternate forms for their Robotic bodies. The idea being, to copy the forms of animals that obviously were able to survive the harsh conditions. Optimus took the form of a gorilla when he arrived on the planet. In robot mode he has jets on his back that he calls Prime Jets, large guns in his wrists and back, and a pair of swords (kept off camera).
Optimus sacrifices himself to stop the Vok planetkiller from destroying earth. His spark is retrieved by friend Rhinox and he (somehow?) gets a new body seeded with transmetal technology. His new body is a purple chrome gorilla with a hoverboard that forms from his calves. In robot mode he has a big mounted set of guns with a bullet-proof shield than comes up from his back and other various weapons.
When he tries to house the spark of the original Optimus Prime in his own body (to keep Prime from going offline) his body is morphed by the Matrix of Leadership and he becomes Optimal Optimus. Much like when Hotrod used the matrix of leadership to destroy the planet devouring Unicron and became Rodimus Prime.
When Optimus finally returns to Cybertron he finds Megatron has taken over using Vehicon drones and a virus that keeps transformers from transforming to robot mode (and puts them in their original non-transmetal bodies. To combat the virus, the supercomputer known as Vector Sigma reformats him and the other surviving maximals into new technorganic bodies. Optimus Primal becomes a technorganic silverback gorilla that can meditate and commune with Vector Sigma (also known as "the Oracle"), commune with the sparks of other transformers, reformat other transformers into a technorganic body, fly with new prime jets, create energy absorbing energy shields and reflect firepower back at enemies, and fire energy disks from his chest.