Cascade

Cascade was once a powerful warrior that served the Decepticons during the war on Cybertron. They worked alongside Starscream, both growing attached to one another during the war.

But, as the war moved to Earth, he begun expressing his want for power over his love for Cascade, causing said warrior to turn sides to spite the other Seeker. 

Over time, Cascade grows to realise just how bad the Decepticons really are and becomes great allies with the Autobots, even taking interest in the three human kids they keep around at times.

Cascade does lash out at times whenever someone brings up their past or speaks as though they judge Cas's original choice in side, but at the end of the day, the Autobots are their new family and will still accept Cascade as one of their own.

Their usual job is to scout areas for both Decepticons and Energon sources, so they're rarely within the base at all, enjoying taking their time with their missions.

After the war moves away from Earth finally, Cascade chooses to stop with their part in the battle, leaving back to Cybertron and seemingly disappearing from the war completely.

Rumor has it, they still visit Starscream every-now-and-then, however, they are not helping him with his part as the new leader of the Decepticons.