Commander Sinclair was the original man in charge of Babylon 5, but left to become an ambassador to Minbar which was kind of a cover for him looking after a group of Minbari and Humans called Rangers. He shared this responsibility with Delen and later with Captain Sheridan when he was told ab out them by Delen. The Vorlons also had a hand in the shaping of the Rangers by providing technology to enable the creation of the ranger fleet of ships called the Whitestar.
Although these people were in charge, Sheridan was the only one who actually wore a Ranger badge. The whole point of the rangers was to keep a low profile and report back on movements of the Shadows and their allies. Many times they were able to come and go to the station delivering reports and details through covert means. Later Marcus is introduced to the cast as a Ranger and provides more insight into their training and abilities.