Now a certain man of the servants of Saul was there that day, detained before Yahweh; and his name was Doeg the Edomite, the best of the herdsmen who belonged to Saul.
"Doeg the Edomite"  (1 Samuel 21:7).  This evil character is mentioned here for two reasons.  (1) He would be the chief actor in the destruction of the entire company of the priests at Nob; and (2) David's recognition of him meant that David was required to get out of Nob as rapidly as possible. Doeg would certainly have notified Saul of David's presence there.