From Ardrana

The whisper of a breeze, the crackle of flame, the crest of a wave, the immovability of stone -- these things are as much a part of the genasi as flesh and blood. The genasi are planetouched beings, the descendants of a union of a Human and an elemental creature (often a djinni, hence the name genasi).

These extremely rare beings inspire more distrust and prejudice than other plane-touched, for public opinion regards them as more alien. In general, they also maintain a contempt for other races and an air of superiority that doesn’t endear them to anyone.

It’s often assumed that genasi of differing elements have a natural racial hatred for one another, simply by the fact of their warring elemental natures. This isn’t true; a single genasi usually resents and dislikes all others of his kind, not just those of different elements. Not surprisingly, two genasi (or more) are virtually never encountered together.

Their elemental nature is often extremely evident. Individuals nearly always display a physical characteristic or two that reveals they are more than simply human -- skin or hair color, a special aura, or some other such manifestation almost always marks them. Further, each type of genasi usually displays personality traits relative to his elemental nature. While each genasi is a complex individual, some remain virtual caricatures of their heritage. Fire genasi are often hot tempered and quick, while earth genasi are slow and methodical.

Note: Genasi originally appeared in this form in the Planewalker's Handbook for the AD&D game from TSR. Their use here is for the purposes of providing context for the campaign only.