Greatest Songwriter of all time

Lots of great choices so far, and I agree with some of them; but I guess we're not sticking to Rock. So, for something different I nominate Franz Schubert and Ernesto Lecuona.

Music: Frank Zappa

Lyrics: Tonio K.

SPRINGSTEEN, Richard Thompson, Brian Wilson.

Kate Wolf, Folk Singer. She was a great-singer/writer. Also,
Alan Jay Lerner & Frederick Loewe, & Oscar Hammerstein II.

To be the greatest songwriter of all time, one must be able meet the highest ranking for the following criteria:
1. Write songs with words and melodies that are popular, easily recognizable, and easily sung by masses.
2. Write songs that influence other songwriters or
create a whole new trend in music.
3. Write songs that have a strong influence on society.
4. Write songs that become classics (songs that remain popular for decades or centuries).

While most of the nominations so far are popular, only a handful have met the above criteria. But the question originally proposed was who was the greatest songwriter of all time. OK, OK, let's narrow it to the past century. The clear cut winner in my opinion is George M. Cohan. What other songwriter has received the U.S. Congressional Medal Of Honor for writing songs that positively influenced so many people during both world wars and the depression?