Answer by taking a quote from the following article:

The Shadow is the name of a collection of serialized dramas, originally in 1930s pulp novels, and then in a wide variety of media, and it is also used to refer to the character featured in The Shadow media. One of the most famous adventure heroes of the 20th century United States, the Shadow has been featured on the radio, in a long-running pulp magazine series, in American comic books, comic strips, television, serials, video games, and at least five films. The radio drama included episodes voiced by Orson Welles. Originally simply a mysterious radio narrator who hosted a program designed to promote magazine sales for Street and Smith Publications, The Shadow was developed into a distinctive literary character, later to become a pop culture icon, by writer Walter B. Gibson in 1931.

In print, The Shadow's real name is Kent Allard, and he was a famed aviator who fought for the French during World War I. He became known by the alias the Black Eagle, according to The Shadow's Shadow (1933), although later stories revised this alias as the Dark Eagle, beginning with The Shadow Unmasks (1937). After the war, Allard finds a new challenge in waging war on criminals. Allard falsifies his death in the South American jungles, then returns to the United States. Arriving in New York City, he adopts numerous identities to conceal his existence.  One of the identities Allard assumes--indeed, the best known--is that of Lamont Cranston, a "wealthy young man-about-town." In the pulps, Cranston is a separate character; Allard frequently disguises himself as Cranston and adopts his identity (The Shadow Laughs, 1931). While Cranston travels the world, Allard assumes his identity in New York. In their first meeting, Allard, as The Shadow, threatens Cranston, saying he has arranged to switch signatures on various documents and other means that will allow him to take over the Lamont Cranston identity entirely unless Cranston agrees to allow Allard to impersonate him when he is abroad. Although alarmed at first, Cranston is amused by the irony of the situation and agrees. The two men sometimes meet in order to impersonate each other (Crime over Miami, 1940). The disguise works well because Allard and Cranston resemble each other (Dictator of Crime, 1941).  His other disguises include businessman Henry Arnaud, who first appeared in The Black Master (March 1, 1932), which revealed that like Cranston, there is a real Henry Arnaud; elderly Isaac Twambley, who first appeared in No Time For Murder; and Fritz, who first appeared in The Living Shadow (April 1931); in this last disguise, he sometimes takes the place of the doddering old slow-witted, uncommunicative janitor who works at Police Headquarters in order to listen in on conversations and to look at evidence.  For the first half of The Shadow's tenure in the pulps, his past and identity are ambiguous. In The Living Shadow, a thug claims to have seen the Shadow's face, and thought he saw "a piece of white that looked like a bandage." In The Black Master and The Shadow's Shadow, the villains both see The Shadow's true face and remark that The Shadow is a man of many faces with no face of his own. It was not until the August 1937 issue, The Shadow Unmasks, that The Shadow's real name is revealed.  In the radio drama, the Allard secret identity was dropped for simplicity's sake. On the radio, The Shadow was only Lamont Cranston; he had no other aliases or disguises.

Who is Allard?
The Shadow's real name is Kent Allard,