The term "regeneration" was not conceived until the Doctor's third on-screen regeneration; Hartnell's Doctor merely described undergoing a "renewal", and the Second Doctor underwent a "change of appearance".
Termet "regeneration" blev ikke affødt indtil Doktorens tredje regeneration; Hartnells Doktor beskrev kun at han undergik "fornyelse", og den Anden Doktor undergik en "ændring af udseende".