Blackbeard was once a member of the Whitebeard Pirates' second division, led by Portgas D. Ace. Shanks had warned Whitebeard that Blackbeard was growing stronger and had only joined the crew to hide behind the immense shadow of the Whitebeard name until he felt strong enough to make his move. This moment arrived when Blackbeard murdered a fellow crew member, leading to his departure and Ace's pursuit of him. Blackbeard was also responsible for the scars around Shanks' eye from a past encounter. Shanks advised Whitebeard to recall Ace from his hunt, concerned about the timing of a confrontation between Ace and Blackbeard.
After Luffy defeated Crocodile in Alabasta, Lafitte attempted to nominate Blackbeard as one of the Shichibukai to replace Crocodile, but Blackbeard needed to build up a fearsome reputation first.
Blackbeard coincidentally found himself on Jaya at the same time as Luffy. The two nearly clashed over their differing opinions on the food at an island tavern but ended up sharing a friendly conversation about pirates and their dreams. Despite their similarities and humorous contrasts, it was revealed during the Jaya arc that Blackbeard sought to defeat a strong pirate to gain notoriety and chose Luffy after learning of his 100 million Belli bounty. However, he failed to capture them as they were blasted away by the Knock-Up Stream, which sent the Straw Hats to Skypiea.
Blackbeard is currently one of the Four Emperors. He lost his position as a Shichibukai after invading Impel Down. Prior to becoming a Shichibukai, he had no bounty, but he earned the title after defeating Portgas D. Ace.
(Source: One Piece Wikia)
