Another roman creation myth (there are a lot of those): romulus is known as the founding father of rome (hence the name), but to get to found his namesake city he did have to kill his brother - what was that brother's name?

His  brother's name was Remus.

Explanation:

The story of Romulus and Remus is an old Roman myth about the foundation of the city of Rome. Romulus and Remus were twin brothers whose mother, a Vestal virgin, was the daughter of a displaced king. Her uncle, who was then the ruler, saw the boys as threat and ordered them to be killed.

Romulus and Remus were abandoned by a river, saved by a deity, suckled by a she-wolf, and finally adopted by a shepherd. They grew up to find out about their true identities and help their grandfather take power back.

When Romulus and Remus set off to found their own city, they weren't able to agree on where it should be founded. Their dispute grew and, according to the myth, Romulus ended up killing his twin brother, founding the city of Rome, and becoming its first ruler.

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explanation: