The Hashtag (#)

QUESTION =  Who invented The Hashtag (#) ?

ANSWER = CHRIS MESSINA 

Chris Messina is an open source and open standards advocate currently residing in U.S.A. Messina is best known for his idea to group messages on social media using a single character HASH (#) , now commonly known as HASHTAGS

He posted the first hashtag on Twitter:

How do you feel about using # (pound) for groups. As in #barcamp [msg]?
— Chris Messina, ("factoryjoe"), August 23, 2007