The Three Musketeers is a novel

Novel

A novel is a book of long narrative in literary prose. The genre has historical roots both in the fields of the medieval and early modern romance and in the tradition of the novella. The latter supplied the present generic term in the late 18th century....

 by Alexandre Dumas, first serialized in March–July 1844. Set in the 17th century, it recounts the adventures of a young man named d'Artagnan

D'Artagnan

Charles Ogier de Batz de Castelmore, Comte d'Artagnan served Louis XIV as captain of the Musketeers of the Guard and died at the Siege of Maastricht in the Franco-Dutch War. A fictionalized account of his life by Gatien de Courtilz de Sandras formed the basis for the d'Artagnan Romances of...

 after he leaves home to travel to Paris, to join the Musketeers of the Guard

Musketeers of the Guard

The Musketeers of the Guard were a fighting company of the military branch of the Maison du Roi, the Royal Household of the French monarchy.-History:...

. D'Artagnan is not one of the musketeers of the title; those are his friends Athos

Athos (fictional character)

Olivier d'Athos de la Fère, Comte de la Fère is a fictional character, a Musketeer of the Guard in the novels The Three Musketeers, Twenty Years After, and The Vicomte de Bragelonne by Alexandre Dumas, père....

, Porthos

Porthos

Porthos, Baron du Vallon de Bracieux de Pierrefonds is a fictional character in the novels The Three Musketeers, Twenty Years After and The Vicomte de Bragelonne by Alexandre Dumas, père. He and the other two musketeers Athos and Aramis are friends of the novel's protagonist, d'Artagnan...

, and Aramis

Aramis

C. René d'Aramis de Vannes is a fictional character in the novels The Three Musketeers, Twenty Years After and The Vicomte de Bragelonne by Alexandre Dumas, père...

, inseparable friends who live by the motto "all for one, one for all

Unus pro omnibus, omnes pro uno

Unus pro omnibus, omnes pro uno is a Latin phrase that means "One for all, all for one" in English. It is known as being the motto of Alexandre Dumas' Three Musketeers and is also the traditional motto of Switzerland....

" ("tous pour un, un pour tous").

The story of d'Artagnan is continued in Twenty Years After

Twenty Years After

Twenty Years After is a novel by Alexandre Dumas, père, first serialized from January to August, 1845. A book of the D'Artagnan Romances, it is a sequel to The Three Musketeers and precedes The Vicomte de Bragelonne .The novel follows events in France during La Fronde, during the childhood reign...

and The Vicomte of Bragelonne: Ten Years Later.