In Roman mythology Mercury was the swift moving messenger of the gods. Mercury is often depicted wearing winged sandals and with a staff with two intertwined snakes around it. However, Mercury was considered to be a problematic planet in Shakespeare's time. In A Winter's Tale (Act IV, Scene 3) Autolycus says "My traffic is in sheets: when the kite builds, looks to lesser linen. My father names me Autolycus; who being, as I am, littered under Mercury was likewise a snapper up of unconsidered trifles". In plain English he was born under Mercury and is probably rather light fingered! In Germany a bargain is something to be snapped up and many stores advertise specially priced items as Schnäppchen (i.e. something to be snapped up). To the Tudors someone born under Mercury was going to inherit a dishonest nature and be something of rogue. In astrology Mercury was also the planet associated with commerce so those involved in buying and selling needed to be quick witted to make a living. In Twelfth Night (Act 1, Scene 5) Feste says to Olivia "Mercury endue thee with leasing, for thou speakest well of fools". Feste is implying Olivia will need to be blessed with subtlety and craft (and possibly even lie a bit) to handle the approaching Sir Toby who is most likely going to drink the household dry, eat all the cakes and cause mayhem. Mercury remains something of a problematic planet to amateur astronomers even today. It is close to the Sun and difficult to see except in the early morning and late afternoon. Stand outside with a telescope in a freezing winter dawn and you will not see a glimpse of Mercury in the sky because of low clouds on the horizon. However, drive to work in the morning and there Mercury will be on the horizon twinkling at you through the windscreen!! I took the photo below on January 12th at West Lexham in Norfolk. I think it is Mercury but it could possibly be Antares.
Although Shakespeare makes many mentions of Mercury in his plays, poems and sonnets it is usually the metal Mercury or the messenger mercury rather than the planet Mercury he is referring to. However in the Tragedy of Romeo and Juliet we are introduced to a character called Mercutio. Like Mercury the planet which rises early in the morning but then disappears as the Sun rises Mercutio rises like shining Mercury in Acts I and II but then is removed from sight in Act III. William Hazlett in his book Characters of Shakespeare's Plays (published OUP 1817 - I have the 1939 edition) writes that "the character of Mercutio is one of Shakespeare's most mercurial and spirited of the productions of Shakespeare's comic muse". Mercutio is Romeo's friend and companion at the start of the play. He is not part of either of the two noble houses and moves freely between them. His comic monologue about Queen Mab is rather risqué and would have endeared him to theatre audiences. Sometimes he speaks in verse and sometimes not. He has a sharp wit and most of his jokes are about sex! In Shakespeare's plays the action usually happens in Act III (except in Hamlet which is mostly words with little action!) and Romeo and Juliet is no exception. Mercutio, who has quick temper, is killed by Tybalt who is then killed by Romeo who is then exiled from Verona. The comedy element of the play disappears with Mercutio's dying breath (a plague on both your houses) and the play becomes a full blown tragedy. I saw the RSC perform Romeo and Juliet at the Barbican in London in 2000. A young actor called David Tennant played Romeo but he was so outstanding an actor that he totally eclipsed the rest of the cast. Mercutio must die for the play to progress and the audience has to like him to feel something of Romeo's grief. Mercutio like his namesake the planet Mercury appears early on in the day, shines brilliantly, creates a strong impression and then fades away.