John Holland was an American psychologist best known for developing the Holland Codes, a theory of career and vocational choice. His model categorizes people and work environments into six types: Realistic, Investigative, Artistic, Social, Enterprising, and Conventional. This framework helps individuals identify their interests and align them with suitable career paths. Holland's work emphasized the importance of matching personal interests with job environments to enhance job satisfaction and success. His theories have influenced career counseling and education, providing a structured approach for individuals to explore their strengths and make informed career decisions.