Nagmas had developed an aggressive space-faring civilisation as of circa 50 BC. They possess FTL technology and are in cold conflict with the Tadsylwinians, another space faring civilisation which accuses them of stelaing their technology.
They appear as tall and lean gold skinned humanoids with a blaskc mane, long pointy ears and horns on their forehead
While offworld, Nagma usually appear in heavily armed shining power armor and use flying robots called Goelderas to do their bidding.
Some two thousand years ago, Nagma were in conflict with another space faring civilisation, the Tadsylwinians. Status on the relations between the two forces is undocumented nowadays.
A nagma mission is beleived to have come to Earth, in northern France circa 50 BC to get a mystical secret weapon or power source but was driven away by a tadsylwinian force and some indigenous celt warriors.
Source: Albert Uderzo, Asterix Universe, Le ciel lui tombe sur la tête. For more critical informations, see wikipedia entry.