When Brian Michael Bendis took over the Avengers titles, he decided to blow up the team. That was literal in more than a few cases, like Jack of Hearts. Hawkeye, who Bendis claimed was his favorite character, died in another massive explosion but emerged later thanks to House of M. These things happen.
But Bendis then brought in a new team that he saw as a chance to do an all-star team like the original Avengers line-up was, but with the all-stars that existed then. Not all of them made sense, and some of them were questionable picks. But among the promotional art was a “new” character called Ronin. Who was Ronin? Well, that depended on what comic you were reading.