Raised alone on Ego’s planet and away from her native insectoid people, Mantis never really learned how to interact with others. Ego found Mantis in a larva state, orphaned on her home world. He raised her by hand and kept her as his own to quell his neurotic behaviors. Ego uses her empathic abilities to ease his mind and help him sleep in his journey to finding his progeny, including his son Peter Quill, AKA Star-Lord.
She meets the Guardians of the Galaxy after Ego saved them from Sovereign soldiers who were attacking them and proceeds to introduce them to her abilities on their way to Ego’s planet.