The premise through the whole "Alien" franchise is that the "chestburster" creatures were biologically engineered by the beings called "Engineers" in the "Prometheus" movies, who also developed the distinctive spaceships. But don't expect the director Ridley Scott to clarify matters. He had a chance to do that in the follow-on to "Prometheus" but punted in favor of "evil triumphs" instead.
The premise through the whole "Alien" franchise is that the "chestburster" creatures were biologically engineered by the beings called "Engineers" in the "Prometheus" movies, who also developed the distinctive spaceships. But don't expect the director Ridley Scott to clarify matters. He had a chance to do that in the follow-on to "Prometheus" but punted in favor of "evil triumphs" instead.