Mandalorian
Mandalorians are not so much a species as a creed; they are beings who live by the Mandalorian Code, which they refer to as "The Way".
Millenia ago, Mandalorians were a warlike faction bent on proving their strength and honour through combat and conquest; over the centuries they conquered their local sector of space and established their dominion, until they were confronted by the Republic and the Jedi Order. The Republic and the Jedi sought to curb the Mandalorians' expansion via conquest, and the two factions found themselves at war with one another. The Jedi, in particular, were an affront to the Mandalorian Code, with their mysterious Force abilities. Over time, the Mandalorians developed weapons and armor to fight the Jedi; a unique ore on their homeworld of Mandalore called Beskar proved resistant to the energy of the Jedi's lightsaber, a fact which turned the tide of the war in their favour.
Thousands of years of conflict between the Mandalorians and the Jedi followed, until the final battle on Mandalore left the surface of the planet devastated and uninhabitable outside of a handful of sealed dome cities. In the aftermath of the war, and even centuries later, the Mandalorians are made to reparations to the Republic and the worlds they attacked during the crusades, and are forced to give up much of their spacefaring technology, keeping them bound to their homeworld. Officially, Mandalore is not a part of the Republic, but they have become isolationist and hostile toward any visitors to their cities. Hatred of the Jedi in particular runs deep in Mandalorian culture.
Mandalorians who do not live on Mandalore tend to be part of small, nomadic clans in the Outer Rim; they earn their living by hiring their services out as mercenaries, bounty hunters, or raiders, but regardless of their chosen means of survival all Mandalorians abide by the Code. Hatred of the Jedi runs deep in Mandalorian culture, and most Mandalorians would not hesitate to attack a Jedi if the opportunity arose.