Tales of Tolgard
The Spelljammer is a legendary ship which looks like a gigantic manta ray, and houses an entire city on its back. All spacefarers (people who live in wildspace) have heard of the Spelljammer but very few have ever seen it themselves. It is this ship that gives its name to spelljamming, spelljamming helms and anything else connected with travel beyond planets. The ship has been reported to have been seen in countless spheres for as long as records go back. Even some groundlings (people who live on planets that have very little or no commerce with spelljamming communities) have legends about it. There are hundreds of conflicting legends about this ship, and an extensive mythology has developed about the ship.
As a living thing (although it does not consume any matter, it does absorb heat and light through its dorsal side and uses them to produce air and food for its inhabitants), the Spelljammer has a complex life cycle and means of procreation. Normally the ship has no captain and wanders the cosmos seemingly aimlessly. When the Spelljammer has a captain, obtained through another complex process, it will create Smalljammers (miniature versions of the Spelljammer) that go forth as its spawn. Apparently there can only be one Spelljammer at any one time. One Smalljammer will mature into a full Spelljammer ship if it is ever destroyed.