Garden gnome
Garden Gnomes exist in The Sims: Livin' Large, The Sims 2 and The Sims 3.
In Livin' Large they can be made at the KraftMatic Woodworking Table. One of the spells in The Sims: Makin' Magic can temporarily bring a garden gnome to life as a gardening gnome, which will take care of plants.
In The Sims 2 and The Sims 3 they can be bought as garden decoration. In The Sims 3, Sims can purchase (through Buy Mode) or find Sleeping Gnome McMulty, and also find but not purchase Mysterious Mr. Gnome in the mausoleum, by fishing, through the Criminal Career track or by other random events. If you have The Sims 3: World Adventures you can find different versions of Mysterious Mr. Gnome in the travel destinations.
In Nightlife, a guest may attempt to steal a gnome from your lawn, though not when your camera is focused on them. If the gnome is stolen successfully, any Sim in the household can retrieve it, and it will appear in his/her inventory.