Who wrote and originally sung Stairway to Heaven?

The song was written by Jimmy Page and Robert Plant and released on the Zeppelin Four album. However the original intro to the song was written by Spirit in 1967. The song toured with Led Zeppelin for a short period before they ultimately fizzled out and Zeppelin became the band that all rock bands are compared, to this day. I believe Plant and Page had authorization to use the intro and were obviously heavily influenced by Spirit as well as several old Blues singers.