Resident Evil 4 has some amazing bosses, and it was hard to choose the best one. Krauser? He's fun, but his death scene is lame. Saddler? Still fun, but too obvious. Salazar? Great, but you can kill him in one hit with a rocket launcher. El Gigante? Well, you fight four of them, they're nothing special...

Del Lago was breathtaking. Not only was he the first boss in the game, he was also undoubtedly the biggest, and it's no wonder Leon could only hurt him with harpoons. Unless you're on 'easy', he takes a fair number of harpoons before eventually giving up, and before then he could have smashed Leon's boat into the water and swallowed him whole.

Just when you think you can relax, and Del Lago is dead, a rope attached to him finds itself wrapped around your legs, and unless you're playing the Wii version, you have to frantically tap buttons unless you want to see Leon getting dragged out of the boat and underwater, where he faces one of the more visually disturbing deaths by drowning.

'Del Lago' actually means 'of the lake'. Just a little trivia.
From: http://screwattack.com/node/18048