It is difficult to say who Cervantes influences were because much of the literature that influenced him was anonymous.  He was probably familiar with many of the Medieval legends and tales including the Arthurian cycle, The Song of Roland, and others.  There were some particularly Spanish cycles of tales including those of Sanchez Ramirez and his grandson, Romero the Monk who was the central figure of a story called the Bell of Huesca.  These probably influenced him.  He was also greatly influenced by his own life and the cultural setting of his time.  In Spain, it was great to be a man of chilvalry but the days of chivalry were ending.  The invention of guns, mercenaries and armies were bringing an end to the age of knights fighting bravely for the damsel in distress.  Cervantes himself was forced to flee Spain for a time, possibly for having participated in a duel.  Like his character he, like many in Spain at the time, had a code of honor that belonged to an earlier age.

Cervantes was a contemporary of Shakespeare but most likely never read or saw any of his plays.  He influenced nearly everyone who came after him.  Don Quixote is considered by many to be the first modern novel. He certain influenced Defoe, Swift and other early novelists. I believe you can also see his influence in Dickens, Tolstoy, and other writers of great novels.