"why is Jesus Christ associated with the guy on the crucifix?"

As someone old enough to be considered a fossil this is hilarious.

The answer being "V for Vendetta" and the "Anonymous Mask" being "What the guy in the movie wore."

Oh yay, the perfect opportunity to share an obscure, useless fact I know.

The origin of the word "Guy", as both a name and a term, is the man, Guy Fawkes. His name is the first record of the word "guy" being used in any context.

Following the gunpowder treason and plot, which was unsuccessful, and of which he was not the leader, he became in/famous for it anyway, so much so that it became an annual tradition to tar, feather, and execute him in effigy. These effigies were referred to as "guys" and would universally portray Fawkes in an unflattering way, being gaudy and made from trash. In reference to these effigies, people began to point at some disheveled looking person and remark, "look at that Guy over there".

As time went on, the expression remained in use, but Fawkes faded from memory. People less familiar with him, his history, and the effigies began using the term "guy" to refer to any man.

I think it's actually the other way around. "Why is Anon Mask associated with Guy Fawkes?"

The answer, as most people in the thread have already pointed out, is the comic/movie V For Vendetta, which an amazing movie everyone should watch.

V, wears a mask of Guy Fawkes's face to both maintain anonymity and link his anti-fascist mission with that of the Gunpowder Plot.

I've never understood this connection. Yes the king was an unelected tyrant oppressing a minority. But if the plot had succeeded not much would change. There would have been a tyrannical unelected catholic king oppressing the protestant minority.

Since when is Guy Fawkes "Anonymous?"

Some movie.

Because of V for Vendetta.

It's more than just V for Vendetta. Anonymous chose the Guy Fawkes mask from the movie V for Vendetta both because it was available and because it represented their activism efforts.