Gregory Quinn is a canon Star Trek character
His Memory Alpha Article is here
In ST-OM, Quinn is a much higher ranking Admiral, and an adjunct to the Chief of Starfleet Operations. Quinn built a role for himself as a thinker, an analyst and an unconventional point-of-view.
Quinn liked to use his own staff officers to explore the structure of Starfleet and uncover unusual or abusive operations.
Quinn's keen eye and machivellian mind allowed him to discover the infiltration of Starfleet Command in 2364. Although he fell victim to the infiltrators, he left enough information in the hands of Jean Luc-Picard to allow the Captain of the Enteprise-D to foil the infiltration.
In 2366, Quinn discovered the Holly Hop Drive project. Although he was not able to penetrate the operation entirely, he was able to raise enough questions so that Starfleet Command allowed him to assign his own officers to the project to monitor implementation.
Quinn was kicked upstairs in 2371, to Chief of Starfleet Operations. He personally selected Jean Luc-Picard to suceed him in his role as Starfleet Gadfly annd Conscience at-large.
By the 2380s, Quinn was retired from Starfleet, although he still did some problem solving work for Starfleet upon occasion.