What do new partners need to disclose to each other when entering a relationship?

I’ve been seeing a lot of threads here and on other subs lately about people getting into relationships while still not telling each other important things, like health conditions. I was really taken aback by one post about a partner not disclosing that he had herpes to a new partner, thinking how it's even possible.

It got me thinking about what’s actually important to know about someone once you enter a relationship. What do you think is essential to know about your new partner, and what should you reveal about yourself, to make the relationship work?

I'll add mine in a separate message.