William Shakespeare coined a number of phrases that we still use today, including (in varying forms) the following from Hamlet.

 

“The lady protests to much, methinks.”  — Gertrude 3.2.218

“To be or not to be, that is the question.” — Hamlet 3.1.57

“To thine own self be true.” — Polonius 1.3.79

"Though this be madness, yet there is method in 't." — Polonius 2.2.195

“The play ‘s the thing…” — Hamlet 2.2.565

“Brevity is the soul of wit.” — Polonius 2.2.92

“There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy.” — Hamlet 1.5.168

“Something is rotten in the state of Denmark.” — Marcellus 1.4.95

“Alas, poor Yorick, I knew him Horatio.” — Hamlet 5.1.161