Mary Lynn Ainsworth was an influential American developmental psychologist best known for her work on attachment theory. Born on December 1, 1913, she developed the Strange Situation procedure, a structured observational study that assesses the attachment relationships between infants and their caregivers. Her research highlighted the importance of early emotional bonds in child development. Ainsworth's findings categorized attachment styles into three main types: secure, anxious-ambivalent, and avoidant. These classifications have significantly impacted the fields of psychology and child development, providing insights into how early relationships can affect emotional and social functioning throughout life. She passed away on March 21, 1999.