A picture frome Transformers Animated, showing Optimus Prime transforming into a big rig.
Transformers Animated - Optimus Prime
In Transformers Animated, the Autobots unlikely guide through Earth society is a brash, energetic 8-year-old girl named Sari Sumdac, the adopted daughter of a robotics magnate. Setting the Autobots up with their headquarters in an old abandoned auto plant on the outskirts of town, Sari not only becomes an "honorary Autobot" by enlightening them on such mysteries of Earth life like megamalls, junk food and basic hanging out, but also becomes a vital team member in their adventures. And even more importantly, the Allspark endows Sari with a very special power, one the Decepticons would love to get their hands on, not to mention the Allspark itself.