Sahuagin

Of all the Seafolk, the sahaugin are true deep water dwellers. Although they have legs, their highly-developed fins and gills allow them to survive and swim swiftly at incredible depths, and they retain only vestigial lungs.
Like all of the Seafolk, they are descended from a variety of progenitors, but came together under the banner of the dark and bloody-jawed shark gods known as the Blood Clouded Waters, and predation is their religion. The Blood Clouded Waters gave them their hunger, and their power over sharks, and protected them from the influence of the Outerfolk.
In pursuance of their devotion to their gods, the sahuagin prey on the Kua-toa and locathah beneath them, and raid the Merfolk and Tritons above in hate and envy. They even, at times, leave the water to raid the homes of shore-dwellers. They have a special enmity for the sea elves, but this is in large part because much of their own heritage is elven and they resent the status and popularity of their kin.
Individual sahuagin who leave this bloody culture and seek a life closer to the surface tend to be either intensely self-effacing and apologetic for their ethnic history, or to adopt a swagger which defies others to confront them.
Sahaugin have no gender roles, establishing their identity purely in terms of strength among the school.