Mortal foe

an inveterate, desperate, or implacable enemy; a foe bent on one's destruction.

See also: Mortal

References in classic literature ?
Admit him,'' said Cedric, ``be he who or what he may; a night like that which roars without, compels even wild animals to herd with tame, and to seek the protection of man, their mortal foe, rather than perish by the elements.
But all of my own sex - especially one impostor, three or four years my elder, with a red whisker, on which he established an amount of presumption not to be endured - were my mortal foes.
The Syrian regime was its mortal foe to the north so no Israeli leader wishes Assad well.
Played by Matthew McConaughey, he is Elba's mortal foe.
What it meant was that they learned to see the US as adversary, rival, or competitor not as a mortal foe.
That summer of 1980 in Washington, DC, Ninoy decided to speak out against his mortal foe, Ferdinand Marcos.
A-Zahar, a long-time mortal foe of Israel - he told BBC in 2003, "I'm telling you frankly, the attitude of Islam is not to accept a foreign state in this area" - blamed Israel for the lack of progress in the talks on the release of Shalit.
This time she's his mortal foe, the Wicked Queen in the same production of Snow White.
Chapter four is about the New Illiteracy, called "The mortal foe of my children".
Lost to England's mortal foe, in those sad, dark days of long ago.
Friends will become mortal foes hacking down reputations.
As the embittered webslinger faces further robot attacks, each deadlier than the last, his spider-sense warns that Jameson himself is behind them, possibly colluding with Electro, Alistaire Smythe, or another of Spider-Man's mortal foes.