According to legend, Wild Bill Hickok was shot to death in the middle of a poker game with 2 pairs: black aces and black eight's. Noone knows for sure what the kicker was, but from then on black aces and eight's has been called dead man's hand.
"Pushing up the ante, I know you've got to see me,
Read em and weep, the dead man's hand again"
~The Ace of Spades, by Mötorhead
Historically, the phrase, "Dead Man's Hand" was given to the last poker hand that Wild Bill Hickok had been dealt when he was murdered during a game of five-card-draw. Although there is quite the controversy over what those five cards were or even if there actually were five cards when the infamous Hickok was slain, there appears to be a general mind that he was holding a pair of 8's and a pair of Ace's. However, the most controversial aspect about the poker hand in question, was the the number and suit of the fifth card.