The largest planet in the universe that we know of is a gas giant similar to Jupiter. It is about 1.4 times as large, but has only about 3/4ths of Jupiter’s mass. HAT-P-1 is located in Lacerta, about 450 light-years from earth. The density of this gas giant is so low that it is less dense than cork. What is intensely interesting is that no current models of gas giant formation can account for something so massive and of so little density. A link can be found below.