Siderenios

Siderenios (/si.ðə.ˈɹɛ.ni.ɔs/ in English and /s̠i.ðe̞.ˈre̞.ni.o̞s̠/ in Modern Greek), also spelled Σιδερένιος and Siderénios''', is a formerly organic robot dragon. Siderenios is most known for being shaped like a dragon and biologically a steam locomotive. They dress in a steampunk style. The time periods of Ancient Greek and Old English do not line up with the industrial revolution and the invention of the train in Earth's timeline, but, notably, this is not Earth, nor meant by Siderenios' creator to be Earth.

Locomotive form
They used to be organic, but around the time the idea of steam engines and vehicles were being realised during the industrial revolution, they experimented with replacing parts of their own body with metallic ones. Now, they are fully steam-powered, eating/drinking fossil fuels and drinking water to produce steam for their engine. They store the fuel in their tail and the water in their stomach. Their engine is in the place where their heart and lungs used to be, and the steam is released through their horns. They shower with lubricant to avoid rusting, and times they haven't used it has resulted in their parts becoming jammed. They can practically live forever due to being able to be repaired (willingly or not).

Backstory
At the time of Siderenios' transformation, the negative effects of fossil fuels were not known, and now, Siderenios regrets what they're become, abhorring the fact that they contribute to global warming much more than most people and in a modern society where everyone is reducing their carbon footprint. Siderenios can't regain their organic form because it's been hundreds of years since their organic parts were removed, and they've long since decomposed.

Siderenios originally spoke Ancient Greek and Old English, but they've had to adapt to the changes of language and culture over time. Their intention was never to become immortal, but because it's so easy for anyone to bring them back through quick repairs, they've outlasted everyone they've known. It would be seen as unethical to let Siderenios pass when they can so easily be brought back without suffering physical pain.