Dumbledore's knowledge of Voldemort
Hey all, I'm working on a fic where I need to know exactly what Dumbledore knew about Voldemort's history/personality, when and how he learned it, and why he thought it important. I'm in the process of rereading the books (must be prepared for November!), but I'm only halfway through HBP right now and my memory is fuzzy on that which I haven't reread yet.
Obviously, a lot of what Dumbledore knew he was able to observe firsthand, such as the memory that Harry sees where Dumbledore visits Tom Riddle at the orphanage. But what about those things he wasn't able to observe firsthand? For example, why had Dumbledore clearly begun to take an interest in Voldemort by the time Voldemort returned to Hogwarts to apply for the DADA position? How much did he know about Voldemort at that point and from whom would he have learned that? In fact, when did Dumbledore even realize that Tom Riddle had begun calling himself Lord Voldemort?
Further to that, when did (or do you think) Dumbledore began to collect the various memories that he showed Harry throughout HBP? Do you think he was sufficiently concerned about Voldemort to have gathered a significant amount of information on him before his reign of terror during the 1970s, or do you think the majority of that information was collected after Voldemort had emerged as a major threat?
How do you think he came to look for information where he did? ex. when did Dumbledore realize Voldemort was descended from Slytherin and thus think to go to Morfin for memories? or why did he go to Slughorn for information? (seems if Slughorn was so ashamed of the horcrux memory to tamper with it that Dumbledore must have had some inkling of what Slughorn knew, in order to pressure Slughorn to give up his memory)
Any and all thoughts are welcome! :D