Nicodemus was a Pharisee and a ruler of the Jews who came to Jesus by night, recorded in John 3, in the conversation that includes the verse John 3:16.
John 3:1-2 in the King James Version reads:
1 There was a man of the Pharisees, named Nicodemus, a ruler of the Jews: 2 The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: for no man can do these miracles that thou doest, except God be with him.
These verses open the account of Nicodemus in John 3. Read it in context at John 3:1-2, or the full chapter at John 3. Encyclopedia entry: en.wikipedia.org/wiki/Nicodemus.