Who wrote the 1972 song "Lean on Me" about friendship?

"Lean on Me" is a song written and recorded by American singer-songwriter Bill Withers. It was released in April 1972 as the first single from his second album, Still Bill. It was a number-one single on both the Soul and Billboard Hot 100 charts, the latter chart for three weeks in July 1972. Billboard ranked it as the No. 7 song of 1972. It was ranked number 208 on Rolling Stone's list of "The 500 Greatest Songs of All Time" in 2010.

Source: Wikipedia