Okay sure, this guy is Death, but that doesn't mean he's a bad guy. Thanatos is actually known for being a good dude, who gently ushers the departed down into the Underworld. In one famous instance, he and his brother Hypnos, god of sleep, ease the pain of the wounded hero, Sarpedon, before they bring his soul to the Land of he Dead. The official title of Thanatos's soul-ushering job is pyschopomp, and Thanatos is generally thought of as a good one.
In the myth of Sisyphus, though, Thanatos is made out to look pretty foolish. To put it frankly, the death god just doesn't seem all that bright. When Thanatos tries to chain Sisyphus up in Tartarus, the crafty mortal fools Thanatos by saying, "Hey, why don't you try these chains on and show me how they work." And Thanatos actually falls for it. Okay, we'd probably better stop ripping on Thanatos now. Gentle psychopomp or no, we'd just as soon he not come for us today.