Mister Mills is the father of Ali Mills. He was seen in the first film, along with his wife, when Daniel LaRusso arrived at their residence in the Hills to take Ali on a date. Also present was their chaperone, Lucille LaRusso. Mr. Mills was wondering what kind of man his daughter's date was, and his assessment was questionable when Mrs. LaRusso's station wagon stalled and she asked Ali to take the wheel whilst she and Daniel pushed it. This signaled Mr. and Mrs. Mills that the LaRussos were a family of little means.
Later, he was having dinner with his wife and daughter at a country club, of which Sid Weinberg was a fellow member. His stepson Johnny Lawrence was there as well, and politely asked the Mills if he may dance with Ali. This was sighted by Daniel, which Johnny saw as a chance to embarrass Daniel. Mr. Mills later expressed his disapproval of Daniel and recommended Ali get back together with Johnny as he thought Johnny was "a smart boy". It was evident that Mr. Mills was not so much thinking of Johnny's intellect as he was trying to steer Ali back towards Johnny likely to ensure her stable financial future, which was obviously to try to marry into Mr. Weinberg's money.
It is unknown if Mr. Mills is still alive, and if he may make an appearance on the Cobra Kai series. However, given the later financial problems of Johnny in his adult years, his opinion of Johnny would have soured. As it apparent Mr. Mills is a man who thinks much about financial security, he would be glad of Ali's decision to find her own path in medicine, although if he is aware of the LaRusso Auto Group he may have had admitted he misjudged Daniel.