Ratchet is the medical officer/engineer for the Autobots, and as such has always been a key member of the team.
He was one of the first to follow Optimus Prime to Earth, and has kept his fellow Autobots' engines running on several occasions.
On Cybertron, Ratchet has a long standing friendship with Wheeljack, and they together they had resolved many of the Autobots problems when facing the Decepticons.
Ratchet, first and foremost, is a medic and is devoted to helping others. He is also a brilliant engineer and often helps Wheeljack with his inventions.
Though he is a medic, Ratchet is a courageous and capable fighter, often seen on the front lines of any conflict with the Decepticons.
Ratchet rarely backs away from a fight, but spends most of his time repairing his damaged comrades.
Ratchet’s original transformation was into a van type Ambulance.
In the 2007 movie, Ratchet was a Rescue Humm-vee.