2.1 Creation

Darkseid was first created by Jack Kirby in 1970 as a New God, an extra-dimensional being from the Fourth World whereas when Jim Starlin created Thanos, he was originally meant to be an Iron Man villain who would eventually become a cosmic villain

2.2 Location

Unlike Thanos who originated from one of Saturn's moons Titan, Uxas

2.3 Version

The most common individual Thanos is the Earth-616 version designated to the reality where he was born. Thanos is not unique in Marvel as there are parallel versions of the same character in alternate universes such as Earth-1610

Darkseid however is usually referred to his Pre-Crisis, Post-Crisis or New 52 version

2.4