Who coined the expression "The face that launched a thousand ships"?

First, the face. In Greek mythology, Helen of Troy was said to have been the most beautiful woman in the world. She was married to King Menelaus of Sparta but was abducted by Prince Paris of Troy after the goddess Aphrodite promised her to him in the Judgement of Paris. This resulted in the Trojan War when the Achaeans set out to reclaim her. She was believed to have been the daughter of Zeus and Leda, and was the sister of Clytemnestra, Castor and Pollux, Philonoe, Phoebe and Timandra.

Now, the catchy phrase. "The Tragical History of the Life and Death of Doctor Faustus", commonly referred to simply as "Doctor Faustus", is an Elizabethan tragedy by Christopher Marlowe, based on German stories about the title character Faust. It includes a well-known speech by Faustus addressed to the summoned shade of Helen of Troy, in Act V, scene I:

"Was this the face that launch'd a thousand ships,

"And burnt the topless towers of Ilium--

"Sweet Helen, make me immortal with a kiss."