Short answers, pulled from the story.
"Here Comes the Sun" was written and sung by George Harrison. He composed it in early 1969 while visiting the country house of his friend Eric Clapton in Ewhurst, Surrey, playing one of Clapton's acoustic guitars in the garden.
The Beatles recorded "Here Comes the Sun" at EMI Studios in London during July and August 1969. It was released on the 26th of September 1969 as the opening track on side two of the Abbey Road album.
Harrison wrote the song after skipping a business meeting at the Beatles' Apple Corps organisation, seeking relief from the administrative pressures of the band's affairs. The lyrics reflect his relief at the arrival of spring and a temporary escape from those obligations.
In May 2023, "Here Comes the Sun" surpassed one billion plays on Spotify, making it the Beatles' most-streamed song and the first song from the 1960s to reach that milestone. By August 2021 the count had already exceeded 700 million plays.
In 1977, Carl Sagan tried to include "Here Comes the Sun" on the Voyager Golden Record but the copyright was held by EMI, not the Beatles themselves. The unclear legal status and EMI's intervention meant the song was not placed on the spacecraft.
Harrison added the Moog synthesiser throughout the track, completing the final Moog overdub on the 19th of August 1969. In the second verse it doubles the solo guitar line, and in the third verse it adds a counter melody an octave above. Authors Trevor Pinch and Frank Trocco describe its "increasing brilliance of timbre" as conveying the sun's increasing brilliance.