Chromedome was constructed cold and originally went by the name Tumbler. Remembrance Day The Fecund Moon
Before the war, during the days of the Clampdown, Tumbler was a mechaforensic scientist in the police force. The poor bugger was nicknamed "Unlucky" because he had to work with Prowl, the most anal, full-autopsy loving officer of all time. Despite Prowl's Prowlness, the two had an ambiguous, more-than-partners relationship (see Notes). Tumbler had a strong interest in mnemosurgery, the science of hacking into Transformer minds and "reading" their memories, and was fascinated by the conspiracy theories of the Institute, a supposed secret group used by the authorities to brainwash dissidents. After Optimus Prime's subsequent appearance and departure from Cybertron, Chromedome chose to join the Rodimus's crew of the Lost Light, alongside Rewind. Prowl, angry with this decision, tried to persuade him to stay, noting that Chromedome was "gifted" and his talents were still required on Cybertron, with the plan regarding Overlord left unspoken due to Rewind's presence. Eventually, realizing he wouldn't get anywhere with the argument, Chromedome gave up left with Rewind, leaving Prowl to fume alone in his office.