These rankings are of personal view! I personally follow few of them out of my interest.
Aaron Swartz always wanted to make internet a safer place. He was charged with violating federal hacking laws for downloading millions of academic articles from a subscription database service that MIT had given him access to via a guest account.
Many mentioned on these videos are well known people in internet security and hacking performed by them.
Please do bit google on them and have a read and it should be interesting for you to know that NOT ALL were criminal or did by intention.