Humans are bipedal ape descendants from the planet Earth. Not noted for being particularly bright, up until they are destroyed, if they even manage to do that much correctly, they actually still think that digital watches are a pretty neat idea, and they spend most of their time concerning themselves with moving about little green pieces of paper. On the bright side, they are rather adept at adapting to just about any situation that the universe tosses at them.
For a short time the last two humans left in the universe, following Earth's destruction by the Vogons, were Trillian, who had left the Earth some time before its destruction with Zaphod Beeblebrox, and Arthur Dent, who escaped the Earth's demolition with a man whom he thought to be human, but wasn't.
The number went up to three for a while, as they had a daughter called Random Dent. Unfortunately, they were all killed in the events of Mostly Harmless.