The Chimera lasts because it gives fear a memorable shape. It is not one danger but several dangers fused together: the open violence of a lion, the uncanny strangeness of a goat in the body, the hidden threat of a serpent, and the distance-making terror of fire.
It also shows that a monster story can be political. Bellerophon is not sent to the Chimera by chance; the creature becomes part of a court's attempt to get rid of him. The myth is about the monster in the hills, but it is also about the danger inside royal houses, sealed letters, and impossible orders.
Today, "chimera" often means a fantasy, illusion, or thing made from mismatched parts. That modern meaning makes sense, but it is richer when the old story stays in view: a creature that should not exist, a hero who should not survive, and a fight that can only be won by changing the angle of attack.