While both Android 21 and Gero were still human and working for the Red Ribbon Army, they two were married and had a son together named Gebo whom they designed Android 16 after.

Is Android 21 Gero’s wife?

It was confirmed that Android 21 is married to Dr.Gero and Android 16 is their son.

Who is Dr Gero’s son?

Gebo, code name Gold, is an elite Red Ribbon Army soldier and the son of the Red Ribbon Army head scientist Dr. Gero. He became Android 16’s template.