Crankcase is a whining, moaning ingrate who hates everyone... and everyone hates him. He delights in the misery of others whether they're Decepticon or Autobot. This attitude began before the war when he worked at the Ministry of Energy as a minial janitor. His fellow workers bullied him, mocking his size and feeble physique. Alienated from society he eagerly joined the Decepticons when war broke out.
It was Megatron himself who rebuilt Crankcase, making him bulkier and stronger. Being a Triggercon his small stature disguises his huge fire power with his shoulder mounted heavy guns.
IDW comics movie continuity
Crankcase retains a lot of his personality, hating everyone and everything and constantly complaining about his orders.
Long ago before the war, Crankcase was part of the defense force on Cybertron under the command of Megatron. He followed when Megatron changed the military stance from protectors to offensive and was present at Megatrons war rally where the military leader demanded the control of all of Cybertron's forces.
Many years later after Megatron and the Allspark was destroyed on the distant planet of Earth, Crankcase made the mistake of complaining about orders in front of the then, Decepticon leader, Starscream. Starscream in a fit of rage smashed Crankcase's vocal processor and threw him into a prison cell full of Autobots. Soon after he, and the four Autobot captives, were strung up on Starscreams replica Allspark and were sacrificed. Each of their sparks were extinguished in an attempt to bring the replica Allspark to life.
Transformers: Dark of the Moon
Crankcase makes is live action debut in the third entry of the Transformers trilogy. He is seen on the freeway chase scene with fellow dreads Hatchet and Crowbar. He is later killed by Sideswipe and Ironhide.