Autobots:
* Optimus Prime: Leader of the Autobots
* Bumblebee: Scout and Optimus's loyal second-in-command
* Arcee: Skilled warrior and close confidante to Optimus
* Bulkhead: Strong and loyal Autobot
* Jack Darby: Human ally and Optimus's friend
* Miko Nakadai: Human ally and Bumblebee's friend
* Raf Esquivel: Human ally and Bulkhead's friend
* Wheeljack: Scientist and inventor
* Smokescreen: Young and reckless Autobot
* Ultra Magnus: Veteran Autobot and former leader
* Ratchet: Medical officer and mechanic
* Ironhide: Veteran warrior and Ratchet's close friend
* Cliffjumper: Scout killed by Megatron in the first episode
* Alpha Trion: Ancient Autobot and mentor
* Elita-One: Optimus Prime's second-in-command in the comics and some other continuities
Decepticons:
* Megatron: Leader of the Decepticons
* Starscream: Second-in-command and scheming traitor
* Soundwave: Megatron's loyal spymaster
* Laserbeak: Soundwave's bird-like drone
* Ravage: Soundwave's panther-like drone
* Shockwave: Scientist and strategist
* Breakdown: Megatron's enforcer
* Knock Out: Decepticon medic and Starscream's ally
* Airachnid: Decepticon warrior and hunter
* Dreadwing: Decepticon warrior and Starscream's rival
* Skyquake: Powerful Decepticon warrior
* Dreadbot: Decepticon warrior (voiced by Peter Cullen, Optimus's voice actor)
Other Notable Characters:
* Orion Pax: Optimus Prime's former identity
* Vector Prime: Ancient transformer and creator of the Matrix of Leadership
* Unicron: The planet-eating Transformer
* The Fallen: Ancient Prime and servant of Unicron
* Megatronus Prime: Megatron's former identity
This list represents the major characters who play significant roles in the story. Many other Transformers appear in smaller roles, including members of the Autobot and Decepticon armies, various human characters, and even some unique characters like the Predacons.
For a more comprehensive list, you can search for *Transformers: Prime* character lists on websites like Transformers Wiki or TFWiki.