Clay Kaczmarek

Subject 16 was an individual kidnapped by Abstergo Industries and forced into the Animus before Desmond Miles. A descendant of Ezio Auditore da Firenze, he is related to Desmond Miles, as indicated by portions of their DNA matching in Assassin's Creed II. It is also revealed that he had an ancestor at the Battle of Gettysburg, in the Roman forum and connected with a Queen Isabella.

Life at Abstergo
The individual known only as Subject 16 was captured by the Templar-front organization Abstergo Industries at some point during the 20th or 21st Century for use in the genetic memory recall program. Kept within the Abstergo Laboratory at all times by Warren Vidic, 16 was kept connected to the Animus for dangerously long periods, sometimes even days at a time. This led to 16 suffering from a severe condition known as the "bleeding effect".

Suffering the bleeding effect, 16 began to explore the memories of his ancestors without the use of the Animus, however his inability to actually control these visions forced Subject 16 into a downward spiral of insanity, eventually culminating in his suicide.

Before his death, 16 was forced by Abstergo to explore the memories of an ancestor named Ezio Auditore da Firenze, who the Templars knew had located the Vault during his lifetime ; 16 never relived the memories of his ancestor visiting the Vault. Draining his body of its blood to paint several cryptic puzzles upon the floor and walls of the Abstergo Laboratory, 16 committed suicide to prevent the Templars reaching their goals.

Legacy
Following his death, the Templars were left without the location of the Vault, but the knowledge that an ancestor of Ezio’s – Altaïr Ibn-La'Ahad – had once held a Piece of Eden. Knowing this, Abstergo kidnapped yet another descendant of Ezio and Altaïr, Desmond Miles. During his incarceration, Desmond spoke often with Dr. Vidic’s assistant Lucy Stillman about many things, including his predecessor; accessing private e-mails, he learned even more. Later still, following Desmond’s escape from Abstergo and the beginning of his journeys through the memories of Ezio Auditore the Assassins learned that Subject 16 had managed to hack the Abstergo Animus before his death, and placed twenty encrypted files, called glyphs, throughout the memories.

Decrypting all twenty files, the assassins’ were rewarded with a genetic memory dated "date classified BCE". The video, what Subject 16 claimed to be “The Truth” showed what appeared to be two free-runners fleeing with a Piece of Eden in hand; they revealed themselves to be named Adam and Eve.

Trivia

 * In the non-canon Assassin’s Creed - French Graphic Novel, Subject 16 appears alive and is referred to as "Michael".
 * Many of the Glyphs have hidden messages in them. All of the decoded ones are stated in this page.
 * It is possible that Subject 16 could have been part of the Assassins, as he refers to the Assassin symbol as "our mark" during one of the Glyph puzzles.