Nimoy will voice Sentinel Prime, who preceded Optimus Prime as the leader of the Autobots.  The character is the very same robot  seen being discovered by Apollo astronauts in the film's teaser trailer.  Apparently, once he arrives Earthside, Sentinel Prime disguises himself as a fire truck and participates in the climactic battle through Chicago.

This won't be the first extraterrestrial shapeshifter Nimoy has played, as he also voiced Galvatron in the 1986 animated feature Transformers: The Movie.

Franchise director Michael Bay considering asking Nimoy to take part in the lamentable second installment, Revenge of the Fallen.  "I was too scared to ask him,” Bay jokes. “Plus, he’s married to Susan Bay, who’s a cousin of mine. So I had to be careful. I’ve met him at family functions. But he told me, ‘I would be honored. I’m glad to be back!’”

The voice of Leonard Nimoy is the latest addition to a cast that includes Shia LaBeouf, Rosie Huntington-Whiteley, John Malkovich, Josh Duhamel, Tyrese Gibson, John Turturro, Dr. Ken Jeong, and Alan Tudyk.  Transformers: Dark of the Moon will almost certainly be the final Transformers film for both Bay and LaBeouf, so if you're a fan, don't neglect to catch the giant robot action in 3D on July 1st.