One day...

...his wife Eurydice was bitten to death by vipers.

Overcome with grief, Orpheus played heartbreaking songs on his lyre.

The gods were moved, and so advised Orpheus to travel to the land of the dead and sing his songs to Hades to bargain for his wife.

So it was that Hades' heart was softened and he allowed Eurydice to leave on one condition - that Orpheus would walk in front and never look back.