Who was the second man mentioned in the Bible?

Answer 1

Cain

Another answer:

There is also the "LORD, Jesus Christ," in Paul's lesson to the Corinthians, regarding the duality of man's present flesh and blood nature and his future "spiritual potential":

"...The first man, Adam, became a living person. But the Last Adam - that is, Christ - is a LIFE-GIVING SPIRIT. What came first was the natural body, then the spiritual body comes later. Adam, THE FIRST MAN, was made from the dust of the earth, while Christ, THE SECOND MAN, came from heaven. Every human being has an earthly body just like Adam's, but our heavenly bodies will be just like Christ's. Just as we are now like Adam, the man of the earth, so will we someday be like Christ, the man from heaven." (I Cor.15:45-49 NLT New Living Translation)