The X-Men's decades-long history is filled with the direct descendants of some of Marvel's many mutants. One of the most prominent second-generation X-Men is Rachel Summers, or Rachel Grey, the alternate reality daughter of Cyclops and Jean Grey. This young mutant was a host to the Phoenix Force, and she was one of Marvel's more competent Phoenix hosts until she was forced to give up the cosmic power that defined her family's lineage.
While Rachel has been a resident of the primary Marvel Universe for years, she began life in the "Days of Future Past" timeline in Chris Claremont and John Byrne's Uncanny X-Men #181, where mutants were mercilessly hunted down and exterminated by Sentinels. Rachel was later explained to have been the product of a reality where Scott embraced Jean's partnership with the Phoenix. Born while Jean was paired with the entity, she gained the same abilities as her mother and a powerful connection to the Phoenix Force.
Following Jean's death, Rachel joined the X-Men, endured the rise of mutant persecution and arrests, and was kidnapped and turned into a brainwashed mutant-hunting Hound. Eventually, her journey led to her trying to reverse the past events to save her future. However, a tragic chain of events instead led to her physical body being transported to the mainstream Marvel Universe. She felt out of place for some time, but eventually, she embraced her new life and even took on the Phoenix Force, hoping to use its power for good and make up for the horrors she committed as a Hound.
Throughout her adventures, Rachel never forgot where she came from. While working with the X-Men splinter team Excalibur, she returned to her dystopian future and saved it by reprogramming the Sentinels to protect all life rather than destroy it. However, during her return home with her team, one of her teammates, Captain Britain, was lost to time. To save him, Rachel took his place, forcing her to split into two timelines during the events of Excalibur #75 by Scott Lobdell and Ken Lashley. To make matters worse, during her trip through time, the Phoenix Force inexplicably left her.
One of these versions was taken far into the future where Apocalypse had finally conquered Earth. In this world, she grew old and took the name Mother Askani, where she went on to help raise her alternate reality half-brother Cable. The other Rachel was led to a distant time where she was depowered and enslaved by a villainous tyrant cyborg named Gaunt. Eventually, the modern-day Cable saved Rachel from Gaunt's future and returned with her to the present-day -- without her Phoenix powers.
While Rachel later wielded a portion of the Phoenix's power psychic and received a non-Phoenix power boost that gave her an even more expansive awareness of the world around her, Rachel isn't as well known or recognized as her mother, but she wields the Phoenix Force as effectively as anyone within the X-Men. Even if she doesn't have it anymore, her psychic skills and potential show that what made her strong with the Phoenix Force in the past was within her all along.