Horatio was an agent in the service of Lord Rymar Royce, The Master of Whisperers. He was tall and bronze-skinned, known for his flamboyant dress and manner of speaking.
Little is known of Horatio's background, but he appeared to have traveled or lived in the Free Cities at some point in his life. He may have also worked as a sailor before becoming employed by Lord Royce.
Horatio played a vital role in informing Rymar Royce of the movements and motives of the Lannisters and their allies before the Ascent of the Lion, allowing the Master of Whisperers to hinder King Harys Baratheon.
Near the end of the second era, Horatio met with Danae Targaryen, ferrying her to and from secret meetings with the Master of Whisperers, and joining her on her voyage to Storm's End.
During the third era, Horatio began trying to undermine Rymar. When the Master of Whisperers discovered this, he had Horatio killed, forcing him to swallow broken glass.
"Lord Royce an' I got a little agreement. 'e teaches me an' houses me, an' I do what 'e wants me to do. Easy jobs mostly, nothin' too terrible. Good man Lord Royce is, gets such a bad reputation though." - Horatio
The man who sat opposite him wore a wide floppy hat of straw which covered his face. Bronze skin peeked out from beneath the leather and sealskin tunic of a clammer, but this man did not deal in clams, Abelar knew. This man dealt in secrets. - Blood and Whispers (Chapter 2)