Dr. Gero created the Androids with the sole purpose of killing Goku and ruling Earth afterward. He created Android 17 and Android 18 which still exist today. Together with them is Android 16, which was destroyed by Cell during the Cell Games. He is definitely a machine because of his machine parts, but how come he used to have a mother?
In a cutscene, it was revealed that Android 16 is really an all-mechanical Android, not similar to Android 17 and Android 18. Though his model was actually based on a living being, and that living being was actually Android 21’s son. It was stated that Android 21 used to have a child. Though it was never revealed how her child died, it is stated that he was dead. For some reason, Dr. Gero based his Android 16 to this child.
So in a sense, Android 21 think that Android 16 can be her son. It is possible that Dr. Gero must’ve forced Android 21 to be his test subject when she was still human. Android 17 and Android 18 were both humans once, with names Lapiz and Lazuli. So it can be concluded that Android 21 was a human before.
It is kinda hard to figure out if Android 21 was once Dr. Gero’s wife or not. Some fans believe that this is the case, some fans find it hard to believe. Would Android 21 become a part of the DB canon? Just like SSJ4, Android 21 is not a part of canon because she was never shown on the anime. But imagine if Akira Toriyama will find some arc that he can fit Android 21 to the canon, that would be amazing. Care for some Ultimate Android showdown?