The Sahuagin of Asmodeus

Asmodeus, before he was an arch-devil, and Lord of the Nine Hells, was a great military general serving the gods.  He would have become a god, if only he had shown compassion to a enemy who many think did not deserve it.

Asmodeus, before becoming a Fallen Angel

Asmodeus and the rest of the angels battled the primordials in the Dawn War, and then when the Abyss was left open by the primordial demise, the Demon Spawn War followed.  As the war dragged on, Asmodeus turned to more ruthless methods to deal with the overwhelming numbers of demons flooding out of the Abyss.  Asmodeus has said he fought true war, where pragmatism overruled political, moral, and any other concern that stood in the way of victory.  This met that he and those under his command drifted away from good or neutrality and down the path of evil.  They committed atrocities unthinkable among the angels, like the genocide of entire species - yet Asmoedus will say that doing so would end the war by a 100 years.  Asmodeus was sure of victory, defeat never entered his mind, but to achieve it he took measures that kept his masters hands clean.

When Asmodeus  was cast out by the angels and gods, he and those under his command became  Fallen Angels.  Asmodeus, cunning and wise beyond measure, made sure that if something bad befell him, then he would leave something behind to remember him by.

The sahuagin are so widely spread across your oceans because of their role in the Demon Spawn War.  They served as trackers of a demon horde dispersing across the globe.  As their numbers dwindled they broke ranks and showed their self-serving tendencies, and weakness.  When I was banished for true war, where pragmatism is the only concern, my sahuagins also changed.  They are a little something I had left in store for the gods if things went sour.

- Asmodeus, conversations with Raxcvillibus, "The Sahuagin"