Gollum is the nassssty creature in The Hobbit and The Lord of the Rings who is in love with the precioussss, my precioussssss.

Strunk and White sez to pluralize an s word:

1. Form the possessive singular of nouns by adding 's. Follow this rule whatever the final consonant. Thus write,

Charles's friend
Burns's poems
the witch's malice

Exceptions are the possessives of ancient proper names ending in -es and -is, the possessive Jesus', and such forms as "for conscience' sake, for righteousness' sake."