What is the name of the protective spirit of the household in Roman culture?

The protective spirit of the household in Roman culture is referred to as the Lar Familiaris. This spirit was believed to be a guardian of the home and family. Each household would have its own Lar, which was honored with offerings and rituals to ensure the family's well-being and prosperity. The Lar Familiaris was a part of the larger group of spirits known as the Lares, who were invoked for broader protection, including that of the community and the land.

In contrast, while the Lares are indeed associated with the home and community, the Lar Familiaris specifically represents the guardian spirit that watches over individual households. The other options, Isis and Mithras, are associated with different religious traditions and deities in the Roman world; Isis is an Egyptian goddess worshipped in Rome, and Mithras is linked to the mystery religion of Mithraism, which emphasized different themes and practices unrelated to household protection. Therefore, the Lar Familiaris is the most accurate term for the protective spirit of the household within Roman culture.