"Commedia dell'arte" literally means "comedy of the professional players". It can be linked to a dramatic tradition of Ancient Rome , the Atellan farce, which dated back to before the expansion of the Roman Empire and the resulting influx of the Classical Greek Theatre. Like commedia performances, the Atellan farce was composed of improv comedy skits featuring stock characters performed by masked actors.
Commedia dell'arte became popular throughout Europe in the 16th century C.E. It was performed by itinerant troupes, with a single exception; one commedia troupe was attached to Louis XIV, "the Sun King", during part of his reign, and had a home in Paris. The practical value of itinerancy and improvised dialogue was that commedia players were able to sneak in political satire occasionally, poking fun at various personages that they would never have been able to get away with poking fun at had the troupe had any sort of script that authority figures could examine and censor, or any vested interest in a single town.
Commedia troupes were composed of both actors and actresses, and were about ten to twelve in number. The plots usually centered on a pair of lovers, the Innamorato and his Innamorata, who did not wear masks. (Sometimes, there was a second pair of these figures as well.) These lovers were invariably young and attractive. They were surrounded by a cast composed of the Capitano, a military man who talked big but was actually a coward; the Pantalone, an elderly man who was something of a dupe and frequently schemed after the Innamorata; the Dottore, a friend of the Pantalone who was always a pedant and occasionally an actual doctor; and the Zanni characters (from which we derive the word "zany"), who played a variety of comedic roles, most frequently those of a group of sly servants. The Arlecchino, or Harlequin, is the most famous example of a Zanni role. The reason that Arlecchino became so well known is that he was made the protagonist of a wide selection of English afterpiece plays produced in the late 17th and early 18th centuries C.E. (The afterpiece was a sort of sketch that followed the main dramatic performance at this point in the history of English drama. Frequently, this sketch involved Harlequin encountering a famous figure from Greek mythology.)
These stock characters were easily identified by their masks and costumes. The Capitano had a sword and a cape, the Pantalone and Dottore wore stockings, breeches, and slippers, and the Arlecchino wore a patched costume that was later refined into the now-famous interlocking diamond pattern. The Arlecchino also had a prop which distinguished him: the slapstick, the purpose of which should be self-evident. From this prop, we derive the modern term "slapstick comedy", and this should give the reader some idea of the level of sophistication involved in the humor of commedia dell'arte.
Chief source for this writeup: The Harcourt Brace Anthology of Drama, 3rd Edition.