Throughout history mankind has always found power and brought feel through weapons. From the nuclear bomb, to tanks, and other machines; humans look for the best weapons and the most powerful ones. These weapons are high priorities for governments, military, and corporations in this movie's world. That lust for the ultimate weapon is the drive for finding the alien in the movie. From the words of Ash himself, him and the corporation wanted the alien to be a weapon on Earth.
"The perfect organism" the words from Ash after he becomes immobilized. The crew learns that this was not a mission for resources but a mission to bring back a weapon. The alien itself is almost godlike and perfect. For example the alien is able to reproduce through any host securing its ability to continue to exist. Another example is the alien's ability to breath and live in other environments. On its planet the environment looks dark and lifeless. The alien was able to still breath outside of its planet in another environment. If the alien was able to live on the ship, it could sure live back on Earth. Also during Ash's talk after being immobilized, he brings up that the alien is nearly impossible to kill making it efficient for different purposes.
Looking back through the film again, it is clear that Ash wants to find the alien, bring it on the ship, and bring it to Earth. Ash in the end is an android doing his job for the corporation and bringing the weapon to them. Coming back to the nuclear bomb, Ash can be represented as the many scientists that created the weapon for the government. In this movie's case the government can be compared to the corporation in control of the ship. The crew ends up being the unfortunate bystanders. The ship needed a crew to move and they were the unlucky people that were picked.
The alien proved throughout the film to be a total killer. Each crew member killed was killed by the alien with ease. Imagine if a being like that was used on Earth under the control of the corporation. The corporation would be able to kill anyone that gets in their way. The alien becomes similar to machines on Earth and no direct humans would be needed to do the job. That was the whole idea of the nuclear bomb. The bomb was used in Japan to prevent more American lives from being lost to end the war. The alien is like the same thing prevented the corporation from losing lives.
When it comes down to it the movie provides how corporations and government have the power. Not even the people on the mission besides the android had any idea what they were sent out to do. The corporation found the best species known alive and wanted to harvest the creature's power. This can be related to any powerful weapon the military today has. The alien was seen as the best of all kinds of weapons and nothing else could beat it.
