Species Raphus cucullatus*
Probably the most famous extinct bird of all time.
Discovered 1505, by Portuguese sailors landing on the island of Mauritius. The dodo's existence was not particularly threatened until the Dutch came to settle the island in 1598. The dodo did not recognize humans as a threat, which made them easy hunting. Dodos did not taste very good, but they were edible, and very easy to hunt; you could simply walk up to then and club them over the head. Sailors used dodo meat to restock their food supplies, although the primary cause of extinction was probably the animals introduced by humans, which disrupted the ecosystem and became feral predators of the dodo; rats, pigs, monkeys, dogs, and cats were particular threats. The last dodo was killed in 1681.
Dodos were pigeons (order Columbiformes), although they were rather large, and flightless. The closest living relative of the dodo is the Nicobar pigeon, although they look nothing alike; the dodo and the Nicobar pigeon’s ancestors diverged 42.6 million years ago. We know this because we have done DNA testing on the shattered remains of a dodo kept it the Oxford University Museum of Natural History. You can see the Oxford dodo head at http://www.encyclopedia.mu/Nature/Fauna/Birds/Extinct/DodoRebuild.htm
Dodo birds were flightless, with small atrophied wings. They were gray, lighter at the head, with a white plume at the tale. They had stubby yellow legs, with thick black claws. Its face was 'bald', with no feathers around the eyes or beak. The beak was long, thick, and hooked, coloured light green or yellow (although some sources say the beak was black). Weight estimates put the average dodo bird anywhere from 13-23 kilograms; since there are no complete skeletons or stuffed birds, it is hard to judge. (This description is a generally accepted conglomeration of written descriptions and sketches.)
We don't know much about the way dodos lived. They lived primarily in the forest, although they may have spent time on the shore, fishing. They are reported to build nests in the long grass, lay a single egg at a time, and guard their nests by pecking at intruders. They ate fish and the calvaria fruit; other than that their diet is a mystery (although they also swallowed stones to aid in digestion).
The Mauritian calvaria tree.
After the dodo went extinct, the calvaria tree** almost followed. The calvaria tree needed its seeds to pass through a dodo’s gut before they can germinate; the juices and grinding rocks in the dodo's stomach triggered something, and without the dodos the trees couldn't sprout. By the 1970s, there were only 13 trees left, all of them over 300 years old. Fortunately, it was discovered that turkeys could also trigger germination, although they would not eat the whole fruit, only the pits. Because the timber of the calvaria tree is economically useful, quite a lot of work went into preparing the seeds; these days the pits may be scrapped by hand, or turned in a gemstone polisher, instead of feeding them to turkeys. The calvaria tree is making a successful comeback.
There is some debate as to how important the dodo was in helping the tree germinate; other extinct species may also have been able to get the tree to sprout. But the dodo did its part.
Etymology and other meanings
The word 'Dodo' may come from either the Dutch dodoor, meaning 'sluggard', or the Portuguese doudo, meaning 'foolish' or 'simple'. The former is the most often accepted.
In English, 'dodo' has also come to be used as an unflattering comment or insult. It may mean either a person or thing who is out-of-date; a person who dresses or acts in a passe manner, or a thing or system that has been red queened. It may also refer to a stupid person.
I find it interesting to note that perhaps the two most famous extinctions caused by humans were both pigeon species (the dodo and the passenger pigeon). This speaks more for humans' fascination with pigeons than any particular Columbicidal urges on our part; we kill all kinds of birds. On Mauritius, 20 other species of bird besides the dodo were driven to extinction.
* Today the dodo is known as Raphus cucullatus. I don't know when it was changed from Webster1913's Didus ineptus. I assume some kind ornithologist took pity of the poor bird and renamed it between now and 1913.
'Dodo' may also refer to two other species, although these are more often called solitaire birds. Each species lived on a different island, and were distinct species. All three are extinct.
** Sideroxylon grandiflorum, formally Calvaria major, AKA the Tambalacoque or the dodo tree.