Shylock's Enemy: Antonio

Antonio

Being business rivals, Shylock and Antonio were natural enemies. However, Antonio's main business is that of a merchant, buying and selling goods and shipping them to other ports, whereas Shylock is a money-lender who makes money by charging interest on loans.
This is not Shylock's job by choice--there were a limited number of jobs which Jews were allowed to do, and this was one of them. However, Antonio has been lending money to people without interest, which cuts into Shylock's business.
It's rather like having a business competitor move in and start giving away the goods you are trying to sell. He's going to put you out of business. Antonio has other resources which enable him to lend money gratis, Shylock has not.
On top of that, Antonio is rude and condescending to Shylock just because he is Jewish. He may not be the most rude and condecending person in Venice toward Jews, but the fact that he is lumps him in with the worst offenders in Shylock's mind