"En alvorlig mann"
Translation:A serious man
Anybody here knows Alvor from Skyrim? I think he is a pretty serious blacksmith.
They're interchangeable in some contexts, but not all.
"Alvorlig" is what you'd use to describe someone's demeanour, and also to describe a serious accident or accusation for instance. It can mean solemn.
"Seriøs" is used to express that you're serious about something; taking something seriously, and is sometimes used to mean professional.