Nearly all of them fleetingly. Is a main character in :-

Mort, Reaper Man

Everybody sees Death once, and normally only once, in their lifetime. There are, however, some exceptions. He can be seen by small children, wizards and cats. 

     He spends his time in his Domain, somewhere absent of time, and sits with his lifetimers draining the sands of existence away. He travels to the Discworld on a horse named Binky, which is in fact a real horse (except for the fact it can travel faster than light and will never die). Death tried using more traditional Skeletal horses, but he found them unpractical and their heads kept on falling off. 

It is thought by many that the real Death comes to only the highest of beings, that is untrue, Death comes to all, regardless of their social status and can only be seen by professional practitioners of magic and people who are about to die or are already dead, and, of course, cats.

Death once had a spell as a human, named Bill Door, who tried his hand at farming for a Miss Flitworth; unsurprisingly, he was very good with a scythe.

He also went AWOL in Soul Music and tried his hand at being a beggar, being an alcoholic and being in the Klatchian Foreign Legion. When all this failed, he just went back to work.