Background
RC-1012 was a Clone born and raised on Kamino. Having been early identified as an outlier among his brothers he was drafted into the Republic Commando program. He was finally assigned to 'Gemini Squad' under RC-1066.
On XXX planet, the drop on planet was messy and RC-1012 got separated from Gemini Squad. He gathered the scattered Clone Troopers (mostly from Monarch Company) that he came across on planet and set up a strong defensive position until the Republic forces could reorganise. The position became a rally point for many more lost forces over the early days of the conflict including Master Ko'Bal. When eventually the injured Clik arrived, he was unable to efficiently lead his own troops leaving RC-1012 as the de facto Clone Commander. He build a strong relationship with Master Ko'Bal during this campaign and when Clik regained his help, Master Ko'Bal found it very hard to ask RC-1012 to relinquish command, causing some tension. RC-1012 also found it very hard to slot back into a non-leadership position when he connected up with Gemini Squad. Luckily for him, after the campaign, RC-1066 was transferred to the ARC, leaving RC-1012 the new Squad Leader of Gemini Squad.
Their paths would cross again as, towards the end of the Clone Wars, Gemini Squad was brought in for behind enemy line harassment actions on Utapau, alongside new Jedi Knight Talas Kochou, technician CT-1010 and their old leader and now personal ARC assignment to Knight Kochou, RC-1066.
When Order 66 was executed, RC-1012 and Gemini Squad turned on Knight Kochou but with the help of CT-1010 and RC-1066, Gemini Squad was killed...or so they thought. RC-1012's head wound was not fatal but instead put him into a deep coma and damaged his chip.
Waking up months later to a new galaxy, the Republic dead and an Empire in its place, RC-1012 found his brothers were not the people he remembered.
Eventually making it through his physical rehabilitation he requested a leave of absence and set off on a journey to find answers...
Motivation
THE REPUBLIC
RC-1012 believes in the Republic and all it stood for. Yes he fought for his brothers, yes he fought for peace, but above all he fought for the Republic. He is determined to restore it in all its glory (and hopefully to what it was before corruption set in).