Gaping Dragon

The  is a boss in Dark Souls. It seems to be a giant dragon split open, with massive teeth protruding out of its stomach and chest.

Location
Found in the Depths.

Summoning
It is possible to summon Solaire of Astora and Knight Lautrec of Carim (assuming the latter has been freed). Solaire's summon sign can be found next to the stairs leading to the white light, while Lautrec's can be found near the Heavy Crossbow. The gaping dragon is also popular for phantom looking for some co-op due to the sunlight medal that can be awarded should Solaire also be summoned.

Strategies
Hitting its head deals extra damage. However this puts one at risk of its charging attack.

After cutting off the dragon's tail, one can stay behind the dragon and will never be hit. Likewise if one attacks the dragon's legs they will be rarely hit as well.

With head up and standing still

 * Sprints and charges in a straight line. Almost an instant death if you are in the way. Can also kill players who follow it too closely when it charges. Recommend letting the dragon stop moving and not rushing behind or to its flank like a mad hollow to avoid damage.
 * Fly straight up, then it either re-rotates itself and lands or tries to land on top of you. Turn the camera to it and keep an eye on it, or look at the shadows directly below.
 * Slams its head down directly in front of it. Pretty much an instant death if hit. Deceptively long range.

With head up and walking towards you

 * Left-arm sweep when you are almost in range.
 * Left-arm stomp when you are almost in range. Stomps three times.
 * Grabs you and eats you. Can catch players by its side.

With head down and standing still
The Gaping Dragon also has a disgusting vomiting attack. It rears back and vomits a massive puddle of digestive fluid and bile that spreads out quite a distance. The vomit damages rating of armor equiopment upon contact.
 * Tail-sweep. Deceptively long range, and probably its second most damaging attack to head slam.
 * Fly straight up to re-position itself or to land on you.