They are supposed to be the baseball equivalent of a seal, that little bit of wax poured onto a finished letter and pressed with a stamp to denote that which is finished. Firemen. Stoppers. Closers. Whatever you want to call them, they are all the rage in the free-agent marketplace.
Here's some perspective from ESPN's Jayson Stark: "Dollars for Kenley Jansen, Aroldis Chapman & Mark Melancon in the last week: $228 million. Total dollars Mariano Rivera earned: $169 million."
According to Cot's Baseball Contracts, the contracts signed by Jansen (Dodgers, five years/$80 million), Chapman (Yankees, five years/$86 million) and Melancon (Giants, four years/$62 million) are the three largest pacts ever given to relief pitchers, not just in total contract value, but also on a per-season basis.