Jack is the Turbo Duel Champion and one of the Legendary Signers bearing the Wings Mark of the Dragon with his signer dragon/ace card being the Red Dragon Archfiend. He is one of Yusei's oldest and closest friends and would help him in his battles throughout the series.
How to Unlock
Jack Atlas Unlock Event: Atlas Rising - The Return of Jack Atlas
They don't. But they ended up doing a lot of stuff I surveyed for: amazoness and destiny hero support, cards at the card trader forever, exp. for events like the tower, more exp. (with reward multiplier), no more hero nerfs, Zane. As long as I don't ask for anything TOO fun, Konami is pretty nice.
Oh, wait. I forgot to mention that I asked them for more e-hero support, too. I never said a word about Jack with beatdown in surveys, though. Maybe they already knew that it was made for the king if no one else asked?