The riddle posed by the Sphinx to Oedipus in Sophocles' play, Oιδίπoυς τύραννoς (Oedipus the King) is perhaps history's most famous:
Which creature in the morning goes on four feet, at noon on two, and in the evening upon three?
The Sphinx strangled anyone who was unable to answer.
However, customs have changed since then and you won't be killed for failing to solve this one. The answer to that riddle came from Oedipus: Man — he crawls on all fours as a baby, then walks on two feet as an adult, and walks with a cane in old age. Finally defeated, the Sphinx threw herself from her high rock and died.
If your appetite for solving riddles has been whetted, here are some to try your hand at - answers are located at the end of this post.
Alive without breath,
As cold as death;
Never thirsty, ever drinking,
All in mail never clinking.
One of Gollum's many riddles for Bilbo in The Hobbit (1937)
I have billions of eyes, yet I live in darkness.
I have millions of ears, yet only four lobes.
I have no muscles, yet I move two hemispheres.
What am I?
The "Minotaur's Riddle", from episode #39 of the Batman Animated Series (1992)
It's a part of Heaven, though it touches the Earth.
Some say it's valuable, others say no worth.
The riddles of the Sphinx from the PC game Heroes of Might and Magic II
With no wings, I fly.
With no eyes, I see.
With no arms, I climb.
More frightening than any beast, stronger than any foe.
I am cunning, ruthless and tall; in the end, I rule all.
Stephen King's Wizard and Glass
I never was, am always to be,
No one ever saw me, nor ever will
And yet I am the confidence of all
To live and breathe on this terrestrial ball.
They follow and lead, but only as you pass.
Dress yourself in darkest black,
And they are darker still.
Always they flee the light,
Though without the sun there would be none.
This thing all things devours:
Birds, beasts, trees, flowers;
Gnaws iron, bites steel;
Grinds hard stones to meal;
Slays king, ruins town,
And beats high mountain down.
Another of Gollum's many riddles for Bilbo in The Hobbit (1937)
And here are the answers for those who need them:
2) The human brain - as Batman explains, "It has billions of optic and auditory nerves, four lobes and two hemispheres, and it's the only thing Edward Nygma (the Riddler) respects."