All this data is potentially out of date, and should be taken with a truckload of salt
The Leviathan class titan is the pride and joy of Caldari engineering. Sporting a bonus for fleet member shield hitpoints, the Leviathan provides excellent support and the possiblity for massive firepower. The Leviathan follows the Caldari color scheme, using a deep gray for it's hull.
After the Dominion expansion, this particular Titan became quite possibly the most powerful ship in existence. Its particular preference of weapons, slot layout and inherent base statistics allow it to acquire a tank and DPS rate that other Titans can only match one of at the same time. Going on the assumption that if a corp can afford a Titan they can also afford the best possible rigs, Commander modules and faction ammo to put on it, as well as the best possible implants available for the pilot and a maxed out fleet boosting gang member, this Titan when equipped with torpedos is able to reach an effective hit point amount of over 40 million, a DPS rate of nearly 12000 from its missles alone with an engagement range of over 60 km, as well as still having the Oblivion doomsday device, a clone vat bay and a jump portal generator.
The Gallente and Amarr Titans have no hope whatsoever of matching both the tank and the DPS at the same time, since their armor tank dependency directly conflicts with the ability to add damage mods to their low slots. The Minmatar's Ragnarok Titan can come close if equipped with Autocannons and faction EMP ammunition, but even at maximum falloff range of its turrets it still has only 65% the engagement range of the Leviathan.
You can see a Leviathan ingame in the Luminaire star system, although it is only a collidable ship and isn't an actual titan.
A Leviathan is a great mythical sea creature of tremendous size. Some historic literature suggests the leviathan to be a flame-breathing creature over 300 miles in length. The leviathan falls into line with Caldari ships in that it's named after a creature.