Titan

Titan is the largest moon of Saturn and is the second largest moon in the system (only behind Ganymede) and the only person other than Earth who has liquid on his surface

he is frequently described as a planet-like moon because he is larger than Mercury. he was discovered in 1655 by Dutch astronomer Christiaan Huygens.

he is primarily made up of ice and rocky material, much as with Venus before the space age, there are liquid hydrocarbon lakes in his poles, he is so smooth, but mountains and several cyrovolcanoes have been found on him.

his atmosphere is largely made out nitrogen, he is the only moon with a thick atmosphere, he likes to have an atmosphere because he doesn't want to show people his surface.

he is friendly, but he never likes Ceres, like what Jupiter does, although his mother Saturn finds him as cute. like Europa, the Moon, and Neptune's Triton, and Uranus' Titania, he likes to play with his feet.

Orbit and rotation
he orbits Saturn once every 15 days and 22 hours, like most moons, he is tidally locked, so he keeps showing his face to Saturn. one of his friends (Hyperion) shares an orbital resonance with him.

Size
Titan is 5,149.46 kilometers in diameter, 1.06 times larger than Mercury, 1.48 times larger than the Moon, and 0.40 times smaller than Earth.

Birth
like Jupiter and Saturn's moons, Titan was born in an accretion disk, people think that he was born when Saturn once had a group of moons similar to Jupiter's, but then they got a series of giant impacts, which led to his birth. though, Rhea and Iapetus where born from the debris of these impacts, such a violent birth explains Titan's eccentricity.

Atmosphere
Titan is the only moon with a thick atmosphere, his atmosphere is a "super rotator" like Venus' atmosphere, his atmosphere rotates faster than his surface, his atmosphere is denser than Earth's atmosphere, his haze layers block the Sun's light and obscure his surface so that his friends won't see his private areas. his atmosphere is made out of 97% nitrogen, 2.7% methane, 0.2% hydrogen, and a couple other trace gases. he spends 95% of his time inside of Saturn's magnetosphere, making him immune to solar winds. in 2013, NASA's Cassini spacecraft detected propene on his atmosphere

in 2014 methane was found on his polar skies.

Climate
his skin is as cold as -179.2 ºC, at this temperature, ice has an extremely low vapor pressure. haze in his atmosphere reflects sunlight out, he receives 1% of sunlight as on Earth.

Surface features
he has been around since the system formed, but his skin is much younger, dating from 100 million to 1 billion years old, his equator is filled with dunes and hummocky. his surface is made out of light and dark terrain, these include Xanadu, a large area about the same size as Australia, it was first identified in infrared light, he has small lakes, one of them is called the Ligeia Mare, a pure methane sea.

Life
he could have hydrothermal vents in his underneath oceans, which may host extraterrestrial life on his surface.

in 5 billion years when the Sun is red giant star, he could be more habitable

In fiction
he appears in many works of fiction, if you wanna see, go to Titan/in fiction

Trivia

 * Titan is the only moon with an atmosphere