According to Gematsu the steam page for Street Fighter V accidentally revealed a video containing the 3 characters which was probably supposed to be a big reveal for fans attending the major fighting game tournament in Las Vegas.
The leak reveals the presence of three classic Capcom stars: Street Fighter's sumo champion E. Honda, Final Fight 3's wily street cop Lucia and, my favourite video game character of all-time, Mad Gear gang member, part-time rock star and pro-wrestling promoter, Poison. During the trailer, Capcom pays homage to his Street Fighter II roots with a play on the original Fighter selection screen in which E. Honda is second on the list. A bundle including all three fighters will supposedly release the very next day. Additionally, E. Honda's iconic "Honda Sento" bathhouse stage has been modernized for SFV: AE and will also be available on August 4th. She makes her comeback following her move to the series in Street Fighter IV. He only makes cameos in Street Fighter 5, but it looks like he will be joining the roster as a playable character next week. Lucia and Poison come with Summer Costumes. She made her Street Fighter debut in Street Fighter III: 2nd Impact but only as a cameo.
The final character leaked in the Street Fighter 5 DLC trailer is Poison. Coming soon to Street Fighter V: Arcade Edition are a couple of old favorites, along with another Final Fight escapee. Poison runs into battle with a far more formidable whip, which makes her a lot more mobile and risky than her Ultra Street Fighter IV rendition. Arcade Edition, however, is a game that you can confidently recommend to anyone.