Trojan Horse

Something that looks like a gift but conceals a hidden attack.

Origin

After ten years of failed siege, the Greeks pretended to sail away, leaving a giant wooden horse outside Troy. The Trojans dragged it inside as a victory trophy. That night, Greek soldiers hidden inside climbed out, opened the gates, and the city fell.

Modern usage

Any concealed threat dressed up as something attractive — including the entire category of malware named after it.

In the wild

The deal looked generous, but the non-compete clause was the trojan horse.— common usage

Achilles' Heel

A single critical weakness in an otherwise strong person, thing, or system.

character

Greek Mythology

Odysseus

The clever Greek hero whose journey home took ten years.