The Lethagoes were a mysterious hybrid species and a mix between Humans and Kalai. Lethagoes were Human in form but quite tall and thin. Nevertheless, they possessed an titanic strength that belied their thin frames. Their faces were thin and pale with a sharp nose, severe eyes and a jutting chin. Their appearance struck some as being quite birdlike, causing a theory to arise that the Kalai were an avian species.
Not much was known about them, and often their Human parents were unaware of the existence of the Lethagoe offspring as was the case of the news reporter, Horatio Varn-Kezzler, who learned that a Lethagoe interviewee of his was actually his own son.
The Lethargoes were primarily encountered at Zirtran's Anchor where they served as representatives of the mysterious Kalai.