Stijen Yol was a red haired joined Trill in the late 24th century, and was host to the Yol symbiont.

From at least 2370, Yol was a field agent of the Federation Department of Temporal Investigations.

In 2381, he also served as a weapons instructor to DTI recruits and taught Teresa Garcia, amongst others, how and when to use a phaser.

Early in 2382, Yol briefed Captain Alisov of the USS Everett prior to an urgent DTI mission to Tandar Prime. (DTI novel: Watching the Clock)