Angel and demon. Eternal enemies from time out of mind, locked in an endless battle.
Mention 'angel and demon' to anyone* and you can almost see the image forming in their minds. A tall angel, with golden halo and hard blue-gray eyes, glowing with righteous wrath, spreads majestic white wings as he raises a flaming sword. The blade is met with another blade, perhaps emitting infra-black light, held by a dark, indistinct being with glowing red eyes and perhaps horns or a curving, pointed tail. Wings black as night stretch behind him.
They certainly wouldn't picture a middle-aged, blue-eyed, blond man in hopelessly outdated clothing standing with a tall, dark, handsome young man in a black suit and sunglasses near a park pond, throwing bits of bread to plump ducks. They wouldn't think of expensive dinners at the Ritz, shared by the same two men, bantering about things both laughably trivial and indescribably cosmic, while making references to ancient Greece and Elizabethan England, or drunken conversations about ineffability and dolphins. They wouldn't imagine luxuriant plants, or an immaculate 1926 Bentley parked outside a second-hand bookshop full of ancient yet lovingly maintained books, or the simple pleasure a cup of well-brewed tea can bring to immortals.
Minds used to imagining winged beings battling can never perceive the bright gold of serpentine eyes peering over stylish black sunglasses, or the way the challenge in them is answered by the compassion in another pair of eyes, blue as the midday sky, that crinkle slightly at the corners; nor will they hear the hidden meanings beneath the light, playful banter of the two immortals.
Angel and demon. Eternal enemies locked in an intricate dance, spinning, coming closer, converging, and whirling away, only to begin all over again.
* - That is, mention 'angel and demon' to anyone who isn't a Good Omens fan. I think that to us, 'angel and demon' has pretty much become synonymous with 'Aziraphale and Crowley'.