J. Ryan, PhD, was a 29th century doctor associated with the University of Copernicus.
Ryan was a member of the Temporal Integrity Commission. Ryan's work with the Commission included the development of the USS Relativity, which was noted on the dedication plaque of that ship. (VOY: "Relativity", dedication plaque)
This character was only mentioned in writing.
This character was named after Voyager actress Jeri Ryan.