Alistair Overeem won the Strikeforce title in 2007 with a win over Paul Buentello, but has not fought in Strikeforce since then. He has also not lost since his last Strikeforce appearance going 6-0-1 over the last few years, while also racking up some wins in K-1.
The title fight will headline the upcoming May 15 show (from what I have read) which will broadcast on Showtime, and Overeem will put his belt up for grabs against Brett Rogers, who last competed in Nov 2009 in a loss to Fedor Emelianenko. IMO Rogers was doing great aganist Fedor until Fedor caught him. Rogers was undefeated until his loss to Fedor.
Another battle of the big men will serve as the co-main event: Andrei Arlovski takes on Antonio "Bigfoot" Silva.