Rookwood is another of the ten Death Eaters to escape Azkaban in Chapter 25. Rookwood is "a pockmarked man with greasy hair" who apparently sold Ministry secrets to Voldemort. (He's also one of the Death Eaters Karkaroff names in Book 4; he used to work for the Department of Mysteries.) Harry sees Rookwood in one of his dreams from Voldemort's perspective.
In the dream, Rookwood explains that Avery is mistaken: the thing Voldemort is looking for cannot be accessed by Broderick Bode. Bode fought the Imperius Curse because he knew that he would be unable to obey Voldemort's commands to take the thing. Voldemort offers Rookwood his gratitude for telling him more about the mysterious thing (clearly, looking back on it, Voldemort is thanking Rookwood for telling him how to access the prophecy he seeks). Rookwood seems pathetically happy to be getting Voldemort's approval.
Rookwood is also present at the Department of Mysteries with the rest of the Death Eaters – of course, since he used to work there, he would've been useful to have around.