Ellen Ryder (neé Harlow) was the wife of Alec Ryder, and mother to the Pathfinder and their twin sibling.
In the 2150s, Ellen was a pioneering designer of implants designed to enhance the abilities of human biotics. Her work eventually evolved into the L2 and L3 implants.
She met Alec Ryder whilst he was stationed in Rio De Janeiro for N7 training and was swept up by his charm.
After the First Contact War, Ellen moved to the Citadel to join Alec during his posting as a military attaché. She later gave birth to twins there in 2163.
Throughout her career researching biotics, Ellen was repeated exposed to Element Zero, which eventually caused her to develop AEND, a rare terminal neuro-degenerative disorder with no known cure.
This spurred Alec to develop illegal AI technology in a desperate attempt to save her. Alec planned to use Ellen's biotic implant research to interface it with SAM with the hopes that the combination could find a cure.
Despite Alec's efforts, it became clear that nothing could be done to save Ellen. She spent the last few hours of her life with her family by her side while encouraging her children to live their lives to the fullest.
Unbeknownst to everyone, including his children, Alec placed Ellen in stasis which suspended any progress of the disease. Alec had her pod brought onboard the Hyperion Ark under the alias "Elizabeth Reilly."
Mass Effect: Andromeda Edit
Through Alec's memories, the Ryder twins locate their mother's cryo pod. Both of them express a desire to wake her up, but because a cure has not yet been found, they are forced to leave her in stasis.
The Pathfinder's dialogue indicates Ellen herself may be unaware of what Alec did, presumably having lapsed into unconsciousness prior to being put in stasis.