The Dooplers were a humanoid species known for involuntarily duplicating themselves (termed "dooplercating") as a defense mechanism against uncomfortable emotions such as embarrassment. As the act of dooplercating was itself regarded as highly embarrassing, a single duplication could easily trigger a multiplicative chain reaction that results in an exponentially increasing number of duplicates. However, once the Doopler regained control of themselves, their duplicates would automatically merge back into one (termed "de-dooplercating").
A Doopler emissary, after "dooplercating"
In 2381, the USS Cerritos transported a Doopler emissary to Starbase 25 for trade negotiations. When they arrived at the starbase, Captain Carol Freeman inadvertently caused the emissary to dooplercate; the situation quickly snowballed out of control, with the duplicates overwhelming a large portion of the Cerritos's saucer section. Eventually, Freeman realized that angering the duplicates with insults would cause them to regain control and recombine. Later, she deliberately set up the emissary to dooplercate again at the Command Conference afterparty. (LD: "An Embarrassment Of Dooplers")
The skeleton of a deceased Doopler remained underneath the Cerritos' hydroponics bay as of 2381. (LD: "Room for Growth")