Asp (snake)
"Asp" is the modern anglicisation of the word "aspis", which in antiquity referred to any one of several venomous snake species found in the Nile region. The specific epithet, aspis, is a Greek word that means "viper". It is believed that aspis referred to what is now known as the Egyptian cobra. Historic representation 
Throughout dynastic and Roman Egypt, the asp was a symbol of royalty. Moreover, in both Egypt and Greece, its potent venom made it useful as a means of execution for criminals who were thought deserving of a more dignified death than that of typical executions. In some stories of Perseus, after killing Medusa, the hero used winged sandals to transport her head to King Polydectes. As he was flying over Egypt, some of her blood fell to the ground, which spawned asps and amphisbaena. According to Plutarch, the Egyptian queen Cleopatra, in preparing for her own suicide, tested various deadly poisons on condemned people and concluded that the bite of the asp (from the Greek word aspis, usually meaning an Egyptian cobra in Ptolemaic Egypt, and not the European asp) was the least terrible way to die; the venom brought sleepiness and heaviness without spasms of pain. Some believe it to have been a horned viper, though in 2010, German historian Christoph Schaefer and toxicologist Dietrich Mebs, after extensive study into the event, came to the conclusion that rather than enticing a venomous animal to bite her, Cleopatra actually used a mixture of hemlock, wolfsbane and opium to end her life. Nonetheless, the image of suicide-by-asp has become inextricably connected with Cleopatra, as immortalized by William Shakespeare:

With thy sharp teeth this knot intrinsicate
Of life at once untie: poor venomous fool
Be angry, and dispatch. —Cleopatra, Act V, scene II
Antony and Cleopatra

Othello also famously compares his hatred for Desdemona as being full of "aspics' tongues" in Act 3, Scene III of Shakespeare's play Othello. Legend
The hypnalis is a legendary creature described in medieval bestiaries. It is described as a type of asp that kills its victim in their sleep. "Cleopatra placed it on herself (at her breasts) and thus was freed by death as if by sleep." See also
Serpent (symbolism)
Snakebite
Vipera aspis

References

Ancient Egypt
Antony and Cleopatra
Cleopatra
Legendary serpents
Reptiles of North Africa
Snake common names
Snakes in popular culture
Snakes of Africa
Suicide by poison
Venomous animals