Why did Diana Rigg leave The Avengers TV series?

Diana Rigg left "The Avengers" TV series after its fourth season in 1969 primarily to pursue other acting opportunities and to avoid being typecast in the role of Emma Peel. She felt that her character had reached its peak and sought to explore a wider range of roles in film and theater. Rigg's departure marked the end of an iconic era for the series, but she continued to have a successful career in acting afterward.