The tight end is a real jack of all trades so more often than not it is shared among more than one player. First and foremost they have to block, but they can also be used as an alternative to a receiver.
When blocking, the tight end is there to protect the quarterback from ambush from an opposition safety or linebacker. If the quarterback is in trouble then the tight end has to be quick on his feet, not only to block but also to release himself from the block in order to give the quarterback an option.
If the play is a running play, the tight end is a fundamental part of the bulldozer that is there to clear a path for the running back, but in order to be available for the throwing plays he needs to be quick too. How many quick bulldozers have you ever seen? Not many, and that’s why the position is shared quite extensively.
If you were to pick out a ‘regular’ tight end you could fairly say that they’re normally tall, but mobile, all-round athletes. And they’re tough cookies too. Stopping the fearsome aggression of a linebacker is no mean feat!