|First appearance||Darkness Rising, Part 1|
|Voiced by||Alexandra Krosney|
Sierra is Jack's crush and a minor character on the show.
Sierra and her friend were at K.O. Burger when they saw Jack Darby talking to a motorcycle. She is surprised that he knows her name. Jack reminds her that he is in homeroom with her, and offers her to take her on a spin. Just then, two Vehicons find them and Arcee runs away with Jack.
Jack challengd Vince to street racing in order to impress Sierra. Jack won the race easily and Vince challenged him to a second one the next day. Both Vince and Sierra were surprised when Jack showed up in a luxury muscle car rather than his motorcycle. The next day Jack gave Sierra a ride on his bike.
Sierra later came to see Jack at work and asked why he was never around town. She was saddened by the fact that he was picked up by a leather clad female on his bike. She remained unconvinced when Jack said the woman was his mom.
- 101. Darkness Rising, Part 1
- 111. Speed Metal
- 201. Orion Pax, Part 1
- 204. Operation: Bumblebee, Part 1
- Sierra was never seen in season 3, but her character is still a part of the show.
- Sierra seems to like Jack, as she notices not seeing him around as much in Orion Pax, Part 1.