The Xantorans were a species native to the planet Xantoras.
They had a very unstable government that was known to change hands every few years. In 2153, when the Enterprise NX-01 visited the planet, the current government had been in power since the late 2140s, but was overthrown by a xenophobic militant group, leading to the visit of the Enterprise to rescue three Denobulan scientists.
When the Enterprise took longer to rescue the scientists than the new government had allotted, a Xantoras ship fired upon them, leading Commander Tucker to suggest that it was just a "kick in the pants" to hurry up to the ship. (ENT: "The Breach")