The X are parasitic organisms discovered on SR388 that can infect any living creature. They kill their hosts and absorb their DNA to assume the host's form. An X that has possessed multiple hosts can combine their appearances and traits during the process of replication and morph into a new entity.

Each game ultimately ends with the Metroids going extinct, with them always returning too. Until Metroid Dread, where the Metroids truly are well and gone...

The species became extinct in the wild at the end of Super Metroid.

He refers to Samus as his "daughter," revealing that his DNA was among the Chozo DNA infused within her when she was first adopted. Raven Beak expresses his disappointment in her disobedience before he and Samus engage in a final showdown.