Four years after “The King Of Mask Singer” premiered on MBC in South Korea, “The Masked Singer” made its U.S. debut on FOX.  The American remake — in all its gaudy splendor — is a bonafide hit. The Jan. 2nd series premiere not only had the highest viewership of any FOX series for its 2018-2019 programming season, but — according to the Nielsen ratings — it was also the most watched series premiere for the coveted 18- to 49-year-old demographics.