Gamma Goblins

Background
Their proper racial name is Grekka, but they are more commonly referred to as Gamma Goblins. They earned their name by virtue of the fact that they look like short, green, ugly humans, much like goblins of human folklore. Specifically, they average around three to four feet in height, have pug like faces, their arms are disproportionately long in comparison to the rest of their bodies and their flesh is a shade of green similar to that of someone who just ate bad fish.

They would be just another footnote in the ever-growing list of space-faring races, except for a few choice facts. Firstly, they are quite stupid. While this would be a mark against them, it actually makes it rather surprising that they made it into space at all. Secondly is their single redeeming quality: an almost supernatural ability to copy objects.
This ability is rooted far back in their culture, nobody knows how far because they dont seem to have a written language. Their one, solitary god, more specifically his priests, preach the seven holy dictums, the third of which is that, if something is found to function, it should be replicated. This has been interpreted to mean that it should be copied, never changed in any regard. For time out of mind, following this teaching, they have built mud huts in exactly the same design, layed out in exactly the same pattern, resulting in identical towns. This has gone on long enough that this trait has become inbred, and it is phenomenally hard for a Grekka to come up with an idea of their own.
They would have remained, quite happily, on their homeworld until their sun went dark, but for sheer chance. A colony ship, the Gulliver, suffered a large interior fire, so bad that it had to land. Mangling itself as it collided into the planet, a percentage of its passengers survived.

It was these beaten examples of humanity that the Grekka first encountered. Knowing only that they came from the mountain that fell from the sky and crushed a settlement, they were convinced from the very beginning that Humans meant them ill. This was not helped when a test firing of the damaged engines accidentally incinerated a few dozen more Grekka. Fairly quickly, it came to blows. Though the humans had guns, the Grekka had numbers, and eventually eradicated the humans from the small planet.
It was then that they began investigating the strange metal mountain that the humans had arrived in. It had been torn asunder by its landing, but was still functional in many ways.
Over a few generations, various things were discovered about it: pressing various lights in a certain pattern made dishes miles away light up with fire. Pressing other lights caused a voice to speak from the ceiling in the strange tongue of the Humans. Over many generations, the Grekka slowly began to understand what some of the systems did.

Eventually, there arose one among them who had the rare, original idea. If the humans came to their world in this mountain, perhaps the Grekka could visit others with it?
They faced many challenges, of course, but slowly a vessel was scrapped together. Using only what they were able to salvage, they soon had a functioning ship, as best they could understand. A tiny fraction of the size of the original colony ship, it wasnt at all aerodynamic, had many exposed and dangerous systems, and was virtually a death trap. Needless to say, the first attempt was an amazing disaster. Though the ship miraculously reached low orbit, it wasnt airtight. Killing the thrusters in panic, the ship fell back to the surface.
The crippled survivors related the problem, and a few more generations passed before the idea came up to seal the ship. Eventually, another wreck of a ship was scrapped together. Despite the fact that none aboard really had any idea of how any of the systems functioned, copying the wiring for the related systems from the colony ship exactly seemed to keep it working just fine.

Unknown to the Grekka, their home planet was in a system that saw a lot of traffic as a trade route. Upon the sight of a unique craft rising from an unexplored planet, the interstellar community did their best to welcome the Grekka.
Now the Grekka dictum of successful things being replicated applies to all walks of life and culture for them. The last time they had encountered another species, they had killed it and in doing so gained the ability to enter space. This behaviour was replicated. Never having the firepower to destroy a ship, their tactic consisted of crashing into it at as high speeds as they could, then killing all aboard. This worked far better than one would have guessed. Eventually, they were able to return to their homeworld in a Frankenstein of a ship that was the result of their suicidal boarding tactics.

Today, the Grekka, predominantly known as Gamma Goblins, exist as a race of marauders. They crash into ships, board them, and proceed to try to integrate the damaged bulk into their existing vessel. The major challenge that they face is their inability to be original, even to the point of wiring systems. If they find a missile system that they wish to use, and the power to it is routed through a gun bank, they will need to copy the gun bank, the power source itself, and any other systems that may be hooked up to that particular power source.
Also due to the fact that they cannot be original, they have a very hard time making repairs, so hard in fact that they would rather rebuild the system from scratch. The end result is that their ships inevitably become hulking leviathans, riddled with redundant systems and slowly rotting from the middle out. Dangerous areas are simply abandoned, and many boarding parties have been lost to the hazardous depths of these labyrinthine vessels.
Unfamiliar with the common tongue and having a hereditary dislike of living creatures smarter then themselves, the Grekka are generally going to be on the wrong side of whatever the local authority is. There is almost universally a bounty on the beings, though the specific amount varies by system.
Their culture, since entering space, has changed in only a few ways. They are tribal, as they always have been, with each tribe keeping a separate ship. There are markings that are unique to each tribe, they vary between tattoos, piercing, actual lacerations and many combinations thereof. The tribes are still ruled over by priests, though their god has changed to reflect their new culture. It is a militant figure, preaching revenge over beings that dare to mock the Grekka by being physically or mentally superior.

Notes
In short, the Gamma Goblins have an unnatural ability to copy an object they have an existing, working sample of. If its not working when they find it, they'll never be able to get it working.

The tribes dont necessarily get along, and they certainly dont function together. They occasionally interbreed however, to stop horrible inbreeding from occurring.

They are usually hostile unless given a good reason not to be, like the unconditional surrender of all your goods, including your ship.