Mantis

Before the war began, Mantis set out to Earth with a group of researchers. She was one of the two scouts that were set to protect the group as they researched the plants and animals of Earth. They lived without incident for years until a group of hunters stumbled upon them. The group tried to make peace with them but they attacked without warning. They managed to kill the researchers, leaving only the scouts.
Mantis's partner, Overboard, tore her away from the fight to the ship and put her in stasis before setting off a distress signal and leaving the ship, making sure none of the humans made it inside.

Mantis stayed in stasis for centuries, even past the war until cybertronians fled to Earth. Megatron sent a group of Decepticons to explore the beacon and see if there was anything of worth, that's when they found Mantis. She was pulled from stasis and basically suffered culture shock as soon as she woke up. Wracked with the grief of her fallen friends and under Megatron's manipulation, she joined the Decepticons and now works as Shockwave's lab assistant and Predaking's caretaker.