Landmine (Unicron Trilogy)

Energon
Landmine is a construction vehicle that lives by a soldier's code. He thrives on honor and loyalty to his comrades and commanders. When Rodimus left Cybertron at the end of the first era, Landmine was one of the Transformers who chose to go with him. Serving as a traffic guard until the war escalated, Landmine boarded Rodimus vessel along with his co-worker and partner, Prowl, a patrol officer. Landmine would become Rodimus' right-hand soldier and his personal bodyguard.

Landmine returned to Cybertron during the Powerlinx Battles to assist Rodimus in reviving Unicron and the Planet Q system. Although Landmine served his commander without question, he was sometimes unsure of their mission agenda. Landmine joined Optimus Prime's team when Rodimus surrendered his leadership to Prime. Landmine is one of the oldest Autobots currently serving the armed forces of Cybertron.

Cybertron
When a massive black hole threatened Cybertron, Landmine was quick to aid his commander in trying to solve this massive problem. Now under the command of Optimus Prime in Rodimus' absense, Landmine has opened up more to his new friends. No longer a stranger to Optimus Prime's men, he has become a soldier and a mentor to the others due to his age, also revealing he once trained Optimus Prime in his youth. At the start, Landmine was attacked by Starscream and was nearly flung into the black hole, only to be saved by a warp-gate from Vector Prime's sword.

Landmine ended up crashing on Earth, marking the first time he would set foot on this planet(Landmine did visit the moon in Energon, but never the Earth). Injured in the crash, Landmine would be found by Coby, Bud and Lori. After being patched up by Coby, Landmine would spend most of the series healing, but eager to get back at Starscream for trying to toss him into the massive black hole.

Landmine, being an elder Autobot, was also the teacher of the soldier Mudflap, who he eventually coaxed back to the Autobot force before they departed for Gigantion. Landmine would be instrumental in obtaining the Giant Planet Key, growing to super-size to defend it from Starscream.

Landmine's Cybertron bio mentions him sustaining damages during the colapse of Unicron, so it's possible that his new smaller form may be the result of emergency repairs.