W.W. Hale the Fifth—or "Hale," if you're besties with this upper-class heist expert—is Kat's partner in crime. And nothing more, okay? Even though he's known Kat for a while, she still doesn't know his first name.
She knows his first name is not "Walter or Ward or Washington [...] Warren [or] Waverly" (2.28). Considering that Hale is basically a teenage Bruce Wayne, we'd suggest Wayne. But Kat thinks that couldn't possibly be it.
Hale and Kat's relationship stems from mutual respect. Kat tried to steal a painting from his house and almost got away with it. Instead of getting mad, he formed a partnership with her. We have a feeling a little romantic attraction had something to do with it, but Kat's too in denial to see this.
Even Gabrielle notices the tension between these two, saying, "Hale's the first guy who could be your boyfriend" (28.26). But Kat's eyes are purely on paintings, not on boys.
Hale and Kat do fight a bit over Nick, the new addition to the group. As with anything between these two, it's difficult to tell if the conflict is professional—Nick's not to be trusted—or personal—Nick's a cute boy moving in on Hale's territory. What if Kat falls in love with him and not Hale?
Kat's pretty nasty to Hale over this Nick business, but they quickly make up, leading to one of the most poignant lines in the book:
[Kat] inched away from the very kind, very funny, very handsome boy who had followed her into the dark, somehow bringing the music with him. (26.22)
That's Hale in a nutshell. He'll follow Kat anywhere, and he always brings some light into her life. We can't help but have a soft spot for the guy.
Hale's butler, Marcus, is someone who deserves a mention here, but not a character page of his own, in our humble opinions. Such is the plight of being "the help." Anyway, Marcus is loyal, the Alfred to Hale's Bruce Wayne (or whatever Hale's real name is). But he has a lot of pent up frustration.
When he gets in on Kat and Hale's heist action, he plays a grouchy old man in a wheelchair who's meant to distract the museum's director. Kat's pretty sure that Marcus isn't acting, though. He's "someone who had several years' worth of snipes bottled up inside of him and was very much enjoying this opportunity to let them out" (31.63).
We guess Marcus has a pretty good gig. Sure, he has to make sandwiches and drive limos, but he gets to travel all over the world. And it's not like Hale verbally abuses him or anything. Still, like most of us, he takes a solid opportunity to vent his frustration at his station in life.