A Death Knight in 5e is a powerful, undead knight created when a doomed, evil warrior is resurrected by dark forces. They are heavily armored and wield dark magic, often bound to a cursed weapon. Driven by hatred, they seek to serve their dark masters or pursue their own malevolent agendas. Death Knights are formidable opponents, combining martial prowess with necrotic spells, and they are immune to many typical weaknesses of the undead.