Simplify the following text for a Grade 15 native English-speaking person.
Original: The character is introduced as a theoretical physicist working at the fictional Black Mesa Research Facility and involved in an experiment which accidentally opens an interdimensional portal , releasing confused , hostile beings into the complex .
Simplified: The character is seen first as a theoretical physicist working at Black Mesa Research Facility and working in an experiment which accidentally opens an portal , releasing confused , harmful aliens into Black Mesa .