Walker was once the footman of Axel Mortmain in London until as late as June 1878. At some point, Walker became one of Camille's subjugates, alongside another darkling called Archer. When Camille first left London, she took Walker with her to Saint Petersburg, while she left Archer with her former lover Magnus Bane to maintain her London residence. Because Camille, as an undead vampire, cannot be tracked, Magnus instead tracked her through Walker with one of his possessions.
Created during the period of time when making subjugates was not yet illegal, Camille was able to keep both Walker and Archer as her subjugates and they remained together for over a century. For this to be possible, Camille fed them her blood in small amounts to keep them healthy and alive much longer than regular humans, which also kept them docile and firmly loyal to the master whom they adored.
In October 2007, he and Archer, under orders from Camille, told the Daylighter Simon that their master wanted to meet with him. When Simon assumed that they were referring to Raphael, the pair did not deny it and instead went along with his assumption until Simon agreed, after which they took him to see Camille. Both Archer and Walker were later killed by the Shadowhunters of the New York Institute during a raid to capture Camille. Upon seeing Archer and Walker dead, Camille cried, stating that both had been with her for 200 years and were like her children.