Tight End

The tight end is has several jobs to do that make it almost impossible for one guy to do the jobs. First, the tight end has responsibilities to block. If there is a cornerback or safety or linebacker trying to sneak in and ambush the quarterback, the tight ends job is to get a good solid hit on this guy and slow him down. If it looks like the quarterback is going to get into trouble due to lots of guys trying to ambush him, the tight end must not only hit one of these guys, but he must then quickly release and get into the open. The tight end will be what is called an outlet receiver - it's his job to catch the ball if the quarterback gets into trouble and has no time to find an open receiver. Finally, the tight end is supposed to be a good blocker so that if the quarterback calls a running play, the tight end can help bulldoze a path for the runner with the ball.
A tight end is therefore usually a big guy so that he's a big target for our troubled quarterback - typically perhaps 6'4" or taller, and about 250 pounds. He also has to be a fast runner, not necessarily Olympic sprinter fast, but pretty fast. And he's got to be a tough guy who can deliver a big hit on an ambushing defender. The tight end will often be sent out to catch passes in the middle of the field, where he will be covered by a couple of linebackers instead of cornerbacks. Linebackers are big guys with bad attitudes who like to torture small animals and scare children, so the tight end has to be a really tough guy to go into their area and try to make plays.
Very few people are capable of being all these things. So we see tight ends in the NFL who specialize in catching the ball and being an outlet receiver, and different tight ends who specialize in blocking and being part of the running game.
A tight end who specializes in blocking will make perhaps $1M to $3M per year. A tight end who is an excellent receiver can make perhaps as much as $8M / year.