1337 speak origins from leet which origins from elite. Leet was just short for elite at that time. People consider being "l33t" is an internet way of being "cool". Like the first example below.
The origin of leet speak is as follows:
leet comes from:
Elite » leet » 1337
Words like "plz" come from:
Please » pleas » ples » pls » plz
Well I got to go » Got to go » gotta
go » got 2 go » gtg » g2g
What's up? » Wasup? » Sup?
I'm laughing out loud! » I'm loling! » lol
I'll be right back » I'll b right back » I'll b rite bac » brb
I own you, I win » You are owned. » (Historic typo word) You got pwned » Total pwnage » Pwned.
So on and so forth. Some of these "leet" internet words come from slang talk just like the example "wasup?". Most people also like to change letter around like "newbie » n00b" same with using numbers instead of letters. Which makes l33t. Some of them also come from the pronounciation of words. Like below:
Are » R
You » U
Cause » cuz
And so on. What makes leet speak so unique is how it has evolved over the years and how it is used in games.
"R U l33t enuff?"
Online game example: "Lets c whu cn m@ke teh most complic@ted l33t spek ev@rr!"
Lets see who can make the most complicated leet speak ever!
"ill brb i g2 put da dawg out 4 a min"
I'll be right back. I have to put the dog out for a minute.
"du u kno wen tha sho strts?"
Do you know when the show starts?