Nea D. Campbell

The 14th (14番目, The 14th), also referred to as "The Musician" or "The Player", was the extra member of the Noah Family and the younger brother of Mana Walker. He was the only member, other than the First Child Road and The Earl, who was able to control the Ark. Before the story's timeline, he gave this power away to a human and ran, betraying the Earl and the Family. The Earl killed him personally. Mana Walker was with the 14th up until then. Sometime before his death, he told Cross Marian that if Mana was looked after, he would return to him one day. Although the exact time is unknown, it is also said that he implanted his memories in Allen before he died. It is speculated by the Order that he chose Allen because Allen was an accommodator of an Innocence. His memories appear to Allen as a portly musician with an erie black face with no features, other than eyes and a mouth. The 14th also has wings in some pictures of him. While the 14th speaks gently to Allen in their encounters, and seems to mean him no harm, it is implied that someday he will consume Allen's body and be reborn. It is also apparent that the 14th's will is to gain revenge against the Millenium Earl upon his rebirth. No motive has been given as to why the 14th betrayed the Earl, nor who exactly the human he gave his powers to is. It is also unknown what sort of supernatural power he possesses, besides the ability to control the Ark. Although the 14th name is not known, it was represented by ***,3 unknown characters.

When Allen Walker is almost killed by an akuma level 4, the akuma sees the 14th Noah inside of him. At first, this is represented by Allen looking calm and smiling in a Noah-ish manner, but shortly after he seems to become a monster reminiscent of a flaming skeleton.

Fan Speculation
WARNING!!! the following is merely speculation, and SHOULD NOT be treated as concrete facts.

It is possible that the 14th's own name (prior to death) was in fact Allen Walker. This could be true because Mana is the 14th's brother and Cross stated that Mana started losing his grip on reality after the 14th's death. The 14th may also represent a memory of Noah that naturally puts him at the opposite of the Earl, such as Sorrow or Remorse.

Navgation
The 14th Noah controls the ark through the piano.