Postby Little Brown Fox » 12 years ago
... Suddenly I think of quadrants. But moving on...
It depends on how you view "robot genetics" whether or not they're related. Nuka and Atom are built from the same blueprints, with slight modifications, but are not considered related; Atlas is the same way, but for some reason, he's considered a relative, even after his "transformation".
2003 Atlas wasn't considered a relative, but could be, since he was built by the same person, while Uran in any incarnation could considered technically unrelated, since she was built by a different person.
Cobalt has only ever had two incarnations, and those were closely related to each other. However, both state different origins for the character. So in his original incarnation, he was not meant to be his "brother", but rather, Atom's successor, should something have happened to him. (Expediting the building process has made him inferior, however.) When they first met, Atom got the impression that they were related, due to their similar appearances, and their ability to call one another. Cobalt, being the naive newborn that he was, latched on to the idea, and they never let go of it.
In Cobalt's second appearance, he was retconned as a failed prototype (although headcanon regards him as only ever being the test model) that came before Atom, but was "shut down" due to his imperfect brain. (He also lacks a lot of his abilities in this version.) However, it is revealed that he wasn't properly shut down, and was, in fact, dumped into the bay along with other assorted experiments and junk in storage. He was regarded immediately as an elder brother, due to his status as a prototype, as well as probably his association with Tenma.