intrude
entrant
persona non grata
unwelcome person
alien
boarder
crasher
encroacher
gatecrasher
infiltrator
invader
penetrator
prowler
pusher
sneak
squatter
stalker
stranger
thruster
unknown
unwelcome guest
adventurer
adventuress
bounder
cad
charlatan
disturber
encumbrance
harlot
impostor
intruder
kidnapper
marauder
mugger
outsider
plunderers
pretender
rapist
renegade
schemer
scoundrel
swindler
timeserver
trespasser
upstart
usurper