Which Roman god was the deified form of Romulus?

The Roman god who was the deified form of Romulus was Quirinus.

Romulus, Rome’s legendary founder and first king, was said to have vanished during a storm or supernatural event while reviewing his troops. According to a tradition reported by Plutarch, the nobleman Proculus Julius later claimed that Romulus appeared to him and declared that he had become Quirinus.

Quirinus was probably an older Sabine or Italic deity who was incorporated into Rome’s early religion. Roman writers eventually identified him with the deified Romulus, linking the city’s founder to a state god. He was served by the Flamen Quirinalis, one of Rome’s major priests.

Quirinus should not simply be equated with Mars. Both had early connections with warfare, but Quirinus became associated especially with the Roman citizen body and the organized community. He also belonged to Rome’s early triad of major gods with Jupiter and Mars, before the better-known Capitoline Triad of Jupiter, Juno, and Minerva became dominant.