The Heartless Control Everything was created in 2002-11.
Heartless Records was created in 2008.
Heartless Moon was created in 2002.
Akuji the Heartless was created in 1998.
Emblem Heartless are artificial Heartless created by Ansem the Wise for his research on Heartless.
Heartless Bitches International was created in 1996.
Heartless - Heart song - was created in 1978.
Heartless - Carriger novel - was created on 2011-06-28.
Sora's Heartless was Pureblood, since it was neither created by Ansem the Wise nor marked with the Heartless symbol.
The Pleasure to Remain So Heartless was created on 2005-04-12.
Heartless - Kanye West song - was created on 2009-09-14.
Because Organization XIII is made up of Nobodies. When a heartless takes control over a person with a strong heart (Sora) a very strong heartless is created. But a Heartless is a person with no will, so it attacks everything with a heart. What's leftover from the Heartless is an empty shell. That turn into a nobody (dusk). Organization XIII are a bunch of powerfull nobodies who have created bodies. They don't have hearts, but they seem to. What I'm saying is that Sora, Kairi, and all those others didn't get turned into heartless untill the end of KH1, so there was no nobody to play as that would be "important" like Roxas, untill the start of KH2!
In KH 1, Ansem the Heartless leads them and Maleficent also leads them. In KH 2, the Organisation XIII and Maleficent can control the Heartless. When in KH 2 Sora asks on which side the Heartless are, Saix answers: "The Heartless ally with whoever's the strongest." So technically, the strongest leads the Heartless... I hope this helped ^_^