What is a description of Antonio from Merchant of Venice?

A figure of romance, Antonio is a patrician of the fabulous city of Venice and a successful merchant. His friends perceive poetry in his extensive commercial ventures:

      ...your argosies with portly said--
Like signiors and rich burghers on the flood,
Or as it were the pageants of the sea--
Do overpeer the petty traffickers 
That cursy to them, do them reverence,
As they fly by them with their woven wings. (1.1.9-14)

He also loans money interest free to people and helps some escape from their debts to Shylock. Because he does so, he incurs the animosity of the usurer Shylock. 

Antonio and Bassanio's friendship is a very strong relationship. While this relationship is often considered homoerotic in modern interpretations, in Shakespeare's time, just as it was even during the 19th century [Henry Clerval and Victor Frankenstein in Mary Shelley's Frankenstein], male friendships were considered the highest and purest forms of love because they were spiritual and cerebral without eroticism.
Because the two men are so close, Antonio suffers from an undefined melancholy and presentiment [another thing Elizabethans strongly believed in], and it is not until later that he learns his dear friend's plight: Bassanio does not have the money to court the beautiful heiress, Portia, with whom he has fallen in love.
So, Antonio, who would do anything for his friend, agrees to lend Bassanio the money he needs. However, since his ships have not yet returned, Antonio does not have the ready money; consequently, he decides to borrow the needed three thousand ducats from Shylock, a man whom he loathes, having even kicked him out of his place of business. Confident that his ships will soon return, Antonio agrees to Shylock's loan and its terms, dictated by Shylock's greed and hatred for Antonio.

When Antonio's ships are lost at sea, he fears that he will have to give up a pound of flesh, but a disguised Portia saves him by pointing out that there is nothing in the agreement that includes blood; the agreement says explicitly "a pound of flesh" only. So Shylock must extract the flesh without making Antonio bleed--an impossibility. Antonio is saved.