Milquetoast
a nobody
a nothing
baby
big baby
chicken
cipher
common man
crybaby
doormat
dud
dull tool
dummy
figurehead
gutless wonder
hollow man
insignificancy
invertebrate
jackstraw
jellyfish
lay figure
lightweight
little fellow
little guy
man of straw
mediocrity
meek soul
milksop
mollycoddle
namby-pamby
nobody
nobody one knows
nonentity
nothing
nullity
obscurity
pansy
pantywaist
pip-squeak
punk
puppet
pushover
runt
sad sack
scrub
shrimp
sissy
small fry
small potato
small potatoes
simple
simpleton
fandango
gymkhana
lawman
snatcher
telex
though