By sheer size, Jool stands the tallest among the local planets, and it ties with Kerbin for the title of richest celestial body (by composition). Its primary color is inexplicably the same as the skin of a kerbal, and the variety among its moons is exceedingly wide and unparalleled to date, making Jool the chief source of inspiration to Kerbal-kind for interplanetary and eventually, interstellar colonization.

Jool is depicted as a Jupiter analog, but its mass is only 80 times that of Kerbin, making it actually smaller than Saturn in comparison.

Rational Resources Classification:

Ocean	Surface	Atmosphere	Exosphere
None	None	Gas (Jovian)*	None

*Gas atmosphere template contains an exosphere template.

From the PDF included in the download:

Bulk Params		Orbital and Rotational Params
Classification	Planet, gas giant	Semi-major Axis	189,765,000 km
Radius	14,000 km sea level	Perihelion	180,276,750 km
Mass	2.99515×1025 kg	Aphelion	199,253,250 km
Gravitational Parameter	1.99899×1015 m3/s2	Orbit eccentricity	0.05
Mean density	2,610 kg/m3	Orbit inclination	1.304°
Surface gravity	1.04 g ASL	Longitude of ascending node	52°
Escape velocity	16,899 m/s	Argument of periapsis	30°
Bond Albedo	0.35	Sidereal orbit period	11.372 years
Solar irradiance	53.2 W/m2	Synodic period	400.19 days
Black-body temperature	111 K	Mean orbital velocity	6,649 m/s
Natural satellites	Laythe	Sidereal rotation period	5.5 hours
	Vall	Solar day	5.5006 hours
	Tylo	Synchronous orbit altitude	13,077 km
	Bop	Sphere of influence	6,745,648 km
	Pol

Atmosphere
Overall height	700 km
Pressure	100 atm sea level, 1 atm @ 161 km
Mean temperature	600 K sea level, 145 K @ 161 km
Mean molecular weight	2.22 g/mol
Composition	90% H2, 10% He