AND fat ..... they turned him from a small green elf into a red fatman, jolly too, thanks to Coke Cola.
Have a look
HERE for the advertising / marketing behind the imagery, and
HERE for the imagery itself.
Having said all that, this was all drawing on pre-existing imagery, of course, but it was with Coke Cola's Christmas advertising that the whole Santa imagery became standardized as a plump human rather than alternatively or simultaneously a green gnome and a red bishop!