Cadet Decker was a Starfleet officer living in the mid-23rd century.
In 2256, Decker was ordered to report to the ready room of the USS Discovery. (DIS: "Into the Forest I Go")
This character was only mentioned in dialogue.
The article "Star Trek Discovery's Coolest, Deepest-Cut Easter Eggs" by StarTrek.com
suggests that it is likely that this cadet may actually be Will Decker