Autobots

• Peter Cullen voices Optimus Prime, the Autobot leader who comes to Earth to destroy the All Spark in order to end the war. Don Murphy decided after discussions with fans on his website that they wanted the surviving voices from the original 1980s cartoon series, The Transformers.^[6] Cullen described reprising the role as easy as "slipping into an old pair of very comfortable shoes that you haven't worn for a while", and was grateful to the fans for wanting him back.^[35] His performance consisted of much improvisation with Bay, and portraying the traditional heroism of the character as well as bringing a sense of humor.^[36] Bay told the animators to seek inspiration from Liam Neeson to inspire Optimus' body language.^[1] Optimus transforms into a Peterbilt truck. The original cab over design was rejected because that would only transform into a twenty-feet tall model of the character, whereas the filmmakers wanted him to stand twenty-eight feet tall.^[1] Optimus has red flame artwork on his blue body. This was a compromise between Hasbro, who wanted to retain the character's iconic red chest, and Bay, who felt red alone would not photograph well.^[21] Hasbro had previously rejected designs of Optimus which were too blue.^[21] Optimus' head was built on set as a prop.^[1]

• Mark Ryan voices Bumblebee for the character's two lines at the end of the film, when he regains his voice. For most of the film's duration, Bumblebee communicates with radio soundbites because of his damaged vocal processor. Before being cast in the role, Ryan had acted as a stand-in for the robots during filming, reading out their lines.^[37] The decision to make Bumblebee silent was inspired by Spielberg's E.T. the Extra-Terrestrial, in order to show that his bond with Sam was beyond words.^[38] The filmmakers had considered using lines from various Paramount films, including "I feel the need for speed!" from Top Gun, but decided such lines would be too obvious.^[39] Credited clips used in the film include John Wayne from El Dorado and Nichelle Nichols as Uhura from the Star Trek television series. A full scale puppet of Bumblebee was also used for the film. The animators modeled Bumblebee's performance on Michael J. Fox.^[2]
  Bumblebee transforms into a 1977 Chevrolet Camaro, and upgrades into the 2009 model.^[2] Bay rejected the character's 1980s form of the Volkswagen Beetle, as it reminded him of Herbie the Love Bug. Hasbro did not mind as long as the car remained yellow. In reference to his original form, the Beetle is parked next to Bumblebee when Sam is buying him.^[21] The modern Camaro was chosen for its friendly appearance,^[2] while the old model was chosen to show that Sam's father could only buy him the cheapest car he could find. In the film, Bumblebee upgrades because Mikaela calls his choice of form "a piece of crap".^[21]

• Darius McCrary voices Jazz, a lieutenant who develops a fondness for urban culture. McCrary said he was honored to follow in the footsteps of Scatman Crothers, who voiced Jazz on The Transformers. "When I was actually [recording], I really did feel Scatman's presence," he said.^[40] Mark Ryan had tried out numerous voices for Jazz, including a Sean Connery impersonation, before McCrary was cast.^[37] Jazz transforms into a modified Pontiac Solstice, a car the director felt was too small, but he decided not to argue with GM.^[20] Hasbro felt it was still a "cool sports car" reminiscent of his original Porsche 935 form.^[21] The screenwriters chose to kill off Jazz as they felt he was the most likable character after Optimus and Bumblebee.^[41]

Alternate modes. Top: Starscream.
Mid, left to right: Optimus Prime, Ironhide, Ratchet and Barricade.
Bottom, left to right: Bumblebee, Jazz.

• Jess Harnell voices Ironhide, who transforms into a modified GMC TopKick C6500 medium-duty truck. The character is a cantankerous weapons specialist. Peter Cullen voiced Ironhide on The Transformers and auditioned to reprise the role in the film.^[42] When Ryan was voicing the character on set, he used a Southern accent as Cullen did.^[37]

• Robert Foxworth voices Ratchet, the team's medical officer. He transforms into a Search and rescue Hummer H2. The writers had wanted to keep his original ambulance form, but the producers wanted something else. Hasbro did not mind if the character was either an ambulance or a fire apparatus.^[9]

Decepticons

• Hugo Weaving voices Megatron, the Decepticon leader who crash-landed in the Arctic thousands of years ago in his quest to obtain the Allspark. When he is defrosted he keeps his original alien jet form out of vanity.^[21] Frank Welker, who played the part on television opposite Peter Cullen, auditioned to reprise the role. Bay considered his voice too soft and felt it would be disrespectful to ask Welker to change it. Weaving's voice had been the inspiration Bay gave to his animators for the character, and the character's voice had become that of Weaving in the director's mind. Weaving recorded his lines in Australia, directed by Bay through iChat.^[1] The deviation from Megatron's 1980s Walther P38 pistol form was done to avoid morphing. Orci and Kurtzman also felt it would be "the equivalent to Darth Vader [becoming] his own lightsaber and having someone else swing him around".^[21] Fans disliked leaked images of the character's head design, so it was redesigned during filming. The prototype design had a much narrower face than the one seen in the finished film.^[21] Optimus calls Megatron his brother; Cullen interpreted this line literally,^[43] but while the writers state this was the case in early drafts, they consider the line in its final context to be metaphorical.^[19]

• Charlie Adler voices Starscream, Megatron's second-in-command. Despite being a popular character, his role is limited because of the film's running time.^[19] A post-credits scene of him escaping Earth was added because audiences at test screenings wanted to know what happened to him.^[1] He transforms into a Lockheed Martin F-22 Raptor jet, which is the successor to his original form, the F-15 Eagle. This keeps the character's role as the powerful and technologically advanced air commander.^[21]

• Reno Wilson voices Frenzy, a small and vicious spy who transforms into a boombox, and later into a mobile phone. Frenzy was primarily animated by one man, who gave the character quirky movements: Bay could tell which shots were not done by him and felt the character totally changed in those scenes.^[1] A puppet was also used on set.^[2] Frenzy was originally named Soundwave, but the writers decided to rename him because he was significantly different from the original character.^[21]

• Jess Harnell voiced Barricade, a Saleen Mustang police car, whom Frenzy guides to Sam. The character was inspired by the G1 Autobot Prowl, because the writers thought a Decepticon displaying authority would use the police car form.^[21]

• Jim Wood voices Bonecrusher, who attacks Optimus on the highway to Mission City. The animators modeled his fighting styles on hockey and football players,^[1] and his alternate form of the Buffalo H Mine-Protected vehicle was modified with a larger fork.^[21]

• For Devastator, the crew chose to use an M1 Abrams tank prop built for xXx: State of the Union.^[2] The character was intended to be named Brawl, but a subtitled Cybertronian line reads "Devastator reporting". It was not fixed despite recognition of the error.^[44]

• Blackout transforms into a MH-53J Pave Low III helicopter, with his minion Scorponok attaching to him. Soundwave had been considered for this role,^[45] with Ravage as his minion,^[38] but Hasbro insisted Soundwave have a music-based role.^[9] Scorponok was chosen after the writers discovered him in the pages of The Ultimate Guide and felt he was appropriate to the setting. A model of his head and tail was built, while primacord explosives were used for his ripple movements in the sand. This was potentially dangerous to cast members, generating genuine terror in the actors' performances.