We all know that Diablo 4 will be set after Diablo 3: Reaper of Souls.
At this point, the gates of heaven have been closed after Malthael, the Angel of Death, destroyed much of Sanctuary. It's through Heaven's ignorance of the events transpiring in Sanctuary that Lilith, the daughter of Mephisto and canonical mother of humanity, is set loose from her prison.
Diablo IV is like the first chapter of a book. We want to tell a big story and we want to tell it, hopefully, for a very long time. Treating this like the first chapter of a book and Lilith as a key character in this story, it feels great knowing that there are still all these other characters that could come back in the future. Or, new characters that we haven’t seen before.
Diablo 4's character customization system will allow players to outfit their characters with hundreds of unique armor pieces as well as detailed facial and body characteristics, so your example of a class won't be the same as someone else's. An expanded dye system will also let players customize individual pieces of armor or entire outfits and items(Check more details on Diablo4items.com).
It's not just armor though. Diablo 4 will let you change the facial features of your character, a new feature for the series. Blizzard says that your characters will get more close-up time than ever before in the series, appearing in lots of different menus, but also in cinematic sequences.
Here are all the details Blizzard mentions in its June 2021 development update:
"You will be able to change the face of your character, the hairstyle, the facial hair (beards and eyebrows), and add jewelry (nose piercing or earrings), makeup, and body markings such as tattoos or body paint. You will also be able to change the color values of your character’s skin, eyes, hair/facial hair, and body markings. Some elements will be class-specific, to support the classes’ unique backgrounds, but many will be shared between classes allowing more possibilities to mix and match."