Grigari

The Grigari are a powerful species from the fringes of the Beta Quadrant. Their culture is based on piracy and, unlike the Ferengi, will resort to unsavory tactics to make profit.

In 2374, a group of Grigari were hired by Obanak Keelen to obtain the Orbs of the Pah-wraith. (DS9 game: "The Fallen")

Alternate timeline
In 2375, the Grigari freed Thomas Riker from his imprisonment on Lazon II. The former Starfleet and Maquis member decided to join the Grigari forces.

By the early 2380s, the Grigari threat had became so serious to the Federation that the USS Enterprise-F was specifically designed to combat them.

Several Grigari forces were invited to Sector 001 in 2388 to take part in trade negotiations. However, the Grigari were confused by a transmission and opened fire. The Enterprise-F was destroyed by the Grigari in the process. (DS9: novel series: Millennium)