Spirit

The Spirits are an advanced race, who defeated the Goa'uld on PXY-887 to protect an Salish Indian tribe. They are a race who can change their form to anything they like and transport persons or vanish them by just waving their arm.

They appeared to the Indians as animals, so the Indians wouldn't be disturbed by their presence. They protected them, guided them and sent them pure Ke (Trinium), from which the Indians would make houses, weapons and probably tools.

When SG-11 was sent to mine the Trinium, they took them prisoner and infilitrated SGC in the forms of SG-11 members. They wanted to destroy SGC, to restore peace to their planet, but after some negotiation, they agreed to just bury the Stargate on their side and show themselves in their true form to the Indians.

Xe'ls, who is a raven according to Indian legend, and T'akaya, who is a wolf according to Indian legend, were Spirits.

They probably just adopted the names from the Indian legends, after they freed them.