For context @Coming it looks like you have a trial business site with us right now
Currently, trial sites get default access to ask.discourse.com via chat, hence you see the discourse_ai user in your DMs. It’s supposed to help you get answers to any Discourse-related questions you might have.
This user is only shown to site admins, you regular community users wouldn’t see it
As Moin has pointed out since it’s an admin user you are unable to delete it. The simplest way would be to either ignore or close out the chat