Our Modern Santa comes from Cartoonist Thomas Nash from the Civil War in America. Thomas Nash also gave us 1. Uncle Sam, 2. The Republican Elephant, and 3. the Democrat Donkey. Note: Nash was a Republican.
Thomas Nast. He borrowed some ideas from Moore.
Norman Rockwell seems to have fixed the red suit, but the European Grandfather Frost was sometimes depicted in red, so all of the ideas seem to go way back.
The real story of St. Nicholas (and his bones), likely Greek from Asia Minor, is as strange as the legend.