Like all great tragic heroes, Othello is flawed. Iago finds this flaw and exploits it. His flaw is his insecurity in his marriage and Iago awakens his jealousy and uses it to destroy him and others.
Since Othello is black and Desdemona is white, her father believes that Othello enchanted her. It is the only explanation he can accept.
In Act I, scene 3, Othello tells the Duke his story. One could say that indeed Othello enchanted Desdemona but not in a negative sense. His personal story was one of adventure and exotic people and places. He had been a slave and was now a great general. Desdemona seemed to hang on his every word and as a result, fell in love with him.
Living the life he had lived deprived him of love and affection. As a result, Iago could exploit this insecurity and arouse his jealousy, aka the green eyed monster.