A humanoid-like Grigari.
The Grigari are a powerful species from the fringes of the Beta Quadrant and may live in a territory that actually borders the Delta Quadrant. Their culture is based on piracy and, unlike the Ferengi, will resort to unsavory tactics to make profit.
They appear to be a form of mechanical based form of life.
The Fallen
In 2374, a group of Grigari were hired by Obanak Keelen to obtain the Orbs of the Pah-wraith. These mercenaries would have numerous encounters with the crew of Deep Space 9. This group of Grigari would be killed on Deep Space 9, either by the Starfleet crew or under the influence of the Pah-wraith possessed Obanak. (DS9 game: "The Fallen")
Millennium
The Grigari feature heavily in the alternate timeline generated by the start of the War of the Prophets. They were encountered when the Red Wormhole was formed and a Dominion fleet was sent into the anomaly to determine whether it connected to the Gamma Quadrant. However, it was learnt that the wormhole actually connected to the Delta Quadrant. All the crew of the ships were believed to have been killed with only Weyoun being the only survivor. He returned to the Alpha Quadrant, changed by the Pah-wraiths, with the Grigari who served as the military arm of the newly formed Bajoran Ascendancy.
The Grigari forces attacked the Dominion and Cardassian force to bring an end to the Dominion War. The offer of surrender was given but was refused. As a result of this, the Grigari wiped out all the worlds of both races leaving nothing standing. 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)