This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
Christopher Pike knew Leland pretty well, although when they met during the red burst investigation he had not seen Pike since before his hair went grey. (DIS: "Saints of Imperfection") One of his operatives, Philippa Georgiou, claimed that Leland was just a puppet following orders. (DIS: "Light and Shadows")
At one point, Leland was involved in an incident where he was "up to his ass" in alligators on Cestus III. He claimed this to be the reason he transferred to Starfleet Intelligence. (DIS: "Saints of Imperfection")
In the mid-2230s, as a young operative, Leland was involved with the time travel research codenamed "Project Daedalus". He worked with Michael Burnham's parents in the project on Doctari Alpha, and blamed himself for their deaths when the Klingons attacked the colony, which claimed their lives. Philippa Georgiou knew that he was responsible for the Burnhams' deaths. (DIS: "Light and Shadows", "The Red Angel")
In 2251, Leland conducted a mission to Deneva that unfortunately involved the wrong ambassador. This incident was kept classified in his secure personnel file, but Georgiou was able to breach the firewall protecting his file to learn this information to later blackmail him to assist the USS Discovery. (DIS: "Saints of Imperfection")
Later on Leland supervised Philippa Georgiou's mission to Qo'noS to shore up L'Rell's regime, and later ferried Ash Tyler and his son to Boreth. Control advised Leland that Tyler would be a strong asset to the organization. Part of Leland's intention had been to recruit Tyler for Section 31, but he left much of that task to Georgiou as well. He told her that she needed to work on her recruitment speech, but she fired back that her speech was just fine and that Tyler was in. (DIS: "Point of Light")
After Spock fled Starbase 5, Captain Leland devoted significant Section 31 resources to find him. (DIS: "The Sound of Thunder") He would eventually capture what would later turn out to be illusory versions of Spock and Michael Burnham created by the Talosians. (DIS: "If Memory Serves")
Memorable quotes Edit
"Is that gray hair I see?"
"Yeah, well, it's one of the trade-offs of having actual hair."
"There are always lives at stake. That's what keep us employed. See, we do what we do so you can do what you do."
Background information Edit
Leland was played by actor Alan van Sprang.
The character first appeared in the "bonus scene" deleted from the season 1 finale "Will You Take My Hand?". In that scene, he was shown to be responsible for recruiting Empress Georgiou into the organization.  He was shown as a Trill in this scene, and Georgiou was able to see that it was a holographic disguise. He subsequently dropped his disguise, showing himself to be Human.