Yamato "Matt" Ishida 

Matt's a cool loner type of kid, who likes to play the harmonica. He's T.K.'s big brother and keeps an eye on the little kid. Matt and Tai fight a lot, usually until T.K. gets upset. Matt is sometimes easily led, for example when Cherrymon convinces him that he should be the leader of the Digidestined instead of Tai and he turns against Tai. However, he'll always come through as a friend - the reason why he holds the Crest of Friendship.

For more info on Matt's family, take a look at the T.K. page.

Later, when we see him at the beginning of Season 2, he's got his own band and calls himself "The Digidestined Formerly Known As Matt".