The Roman god who personified the Sun, distinct from Apollo, was Sol.
Sol was the Roman personification of the Sun and a solar deity in his own right. His name simply means “Sun” in Latin, and he was commonly depicted with a radiant solar disk or riding a chariot across the sky. His Greek counterpart was generally Helios, not Apollo, although Greek and Roman traditions sometimes connected solar imagery with Apollo as well.
Sol’s worship is recorded in Roman religious calendars and included festivals for Sol Indiges, an early or native form of the deity. Later Roman tradition emphasized Sol Invictus, “the Unconquered Sun.” Older scholarship treated Sol Indiges and Sol Invictus as separate, successive gods, but modern discussions often stress continuity and note that ancient evidence does not consistently distinguish them.
Apollo is the key common mix-up. Apollo became strongly associated with the Sun in later Greek and Roman culture, especially through identification with Helios, but that does not erase Sol’s separate Roman identity. Sol was also linked with Luna, the Moon goddess, and dies Solis—“the day of Sol”—helped give Sunday its name in Latin-based terminology.