X-Ray Dog would be the most likely candidate, having made well over 2000 songs in over 40 albums and still in the process of making more. As they are not reliant on any one group of people, they will probably continue making songs indefinitely. Strangely, these albums are not available commercially. Link.
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Sean T Wright has released 104 albums since 1976, and has recorded over 1000 songs. Link
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Elton John has made over 300 songs, just over 30 albums. Link.
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R. Stevie Moore has released over 100 albums and has made thousands of songs. Link.
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Most number-one hits
The Beatles hold the record for the most number 1 singles.
The Beatles with 20
The Jackson 5.
Beatles
an orchestral group im guessing
RBD
George Strait. He is referred to as the "King of Country". George Strait holds the world record for more number-one hit singles than any other artist in the history of music on any chart or in any genre, having recorded 59 number-one hit singles as of 2012.
Typically it would be the young adult age with new music coming out frequently and the most motivation to buy the music.
alabama
The Who
The Carpenters
Faith Hill is most famously known for being a country music singer who has had many number 1 singles. She is married to fellow country music star Tim McGraw.
On the Hot 100 chart, it is Mariah Carey, with 18. Diana Ross has 18 #1 singles to her credit, but 12 of those are credited to The Supremes.
the beatles
an orchestral group im guessing
The Beatles
their music
Faith Hill is most famously known for being a Country Music singer who has had many number 1 singles. She is married to fellow country music star Tim McGraw.
These days most singles have videos.
The Knack was a rock music group from the 1970's and 1980's. They are most famous for their song "My Sharona," which was an international number one hit in 1979.
Ac/dc