The Red Xenomorph (or "Red Alien") are a mutated strain of Xenomorph that rebelled against the primary hive in an attempt to claim dominance over their species.
With the exception of their color, the Red Alien bares identical resemblance to the traditional Xenomorph. According to some sources, they were also more aggressive and reproduced much slower than their primary counterpart.
This deviant breed were produced following the death of the Queen Mother, when several aberrant Elite Guards sought to create their own hive. These Elite Guards worked together to develop a cocoon containing the first Red Queen that would raise an army to challenge the black Xenomorphs.
After massive casualties on both sides, the Red Xenomorphs ultimately lost this war following the involvement of the Colonial Marines when they killed the Red Queen.