A burglar is someone who wears a skee-mask when he is not skeeing (which is against the law in Canada) to cover his bad-looking haircut which he resents because his mom made him get it cut.
Burglars tend to like robbing people's houses that are trailers, because they can steal them (hence the name "mobile home", which was coined from them doing this), but prefer mansions if they can afford the right firearms to attack properly, instead of trying to block flying bullets with a 3-inch long knife.
Burglars have existed ever since man was created, just about it, and it included when the burglars would steal valuable jewels from the women (though still no one really cares to this day) and men (oh crap, nevermind, lots of people care now) in Egyptian times, which would get them arrested by any police cars riding along the road who happened to spot them doing this. And it happened more than you thought it would.
Now, people are robbed and often hurt because burglars feel like that stealing a burger from the McDonalds bag sitting on the kitchen counter isn't enough, and so they want more.