I have a co-worker who is a slacker. They avoid as much work as possible and have no work ethic. It makes me crazy
A slacker ? Is that another term for a lazy individual?
Yes, it is. I think it's funny that the term dates back to about 1790. I can't picture people talking  like that back then.
So who first couch the word?
I'm not totally sure about that, but it started to be used in the US during WWI. People who avoided military service were slackers and the attempts to track them down were called "slacker raids"