A Germaphobic P.I. in Mexico City who has "a taste for clothing loud as a thunderbolt," Mercado is considered "the smartest detective in Mexico." Battling mystery as well as the corrupt Colonel Gomez of the Federal District Police, Mercado is is the first of his kind in popular fiction.
Written by D.L. Champion, this eccentric P.I. appeared in a number of stories published in the 1940s in the pages of Dime Detective, the prestigious crime pulp second only to the legendary Black Mask in its impact on the genre.