The last androids Twilight Sparkle personally worked on prior to leaving CyberLife were a unique pair of RK200s intended to serve as companions for an old and aging friend of hers, an over 3000-year-old dragon named Spike. These two were created to be children just as much as they were caretakers for their owner, and as such were made to have a lot more personality than the average android. They go by “Rainbow Dash” and “Applejack” in non-android contexts, and are rumored to have been inspired by some of their creator’s friends some three thousand years prior – most likely the Elements of Loyalty and Honesty, Firefly and Apple Spice, though these rumors are unconfirmed.
I would say AJ represents Markus while RD represents North.