The original Xeen Arrow was a one time character created by Jack Kirby and France Herron for Green Arrow. He was the superhero protector of Dimension Zero, a world inhabited by telepathic super-giants. In his secret identity he is a leading scientist. Green Arrow and Speedy met him when they were accidentally transported to his dimension. Despite being tiny in comparison, they assisted him in arresting a duo of bank robbers. He then helped them return home, explaining that the passing of a comet had caused the dimensional rift allowing them to enter and the hole would only last for seconds more before he fired them into it on one of his arrows.
Xeen Arrow reappeared in the Super Powers back-up series by Tom Scioli as the hallucination (or not) from the stranded Oliver Queen.