not knowing who this is, much less his(?) nickname, all I can do is hazard a few guesses:

jobbernowl? mome? buffoon?
addlepate? sumph? sawney?
nincompoop? ninny? ninnyhammer?
nupson? mooncalf? footler?
numskull? nimshy? clodpoll?
gowk? balatron? clodpate?
clumperton? coof? dizzard?
chowderhead? chucklehead? dolt?
gawkhammer? gomeril? goop?
grinagog? grobian? gudgeon?
gump? hoddypeak? lobcock?
looby? loord? mome?
mook? puzzlepate? quoob?
tawpie? tomfool? witling?
jackpudding? zob?
les fous font les festinas et les sages les mangent?