Which artist was Van Gogh's cousin and first painting instructor?

Anton Mauve was Van Gogh's cousin-in-law and his first important painting instructor. Mauve was a successful Dutch realist painter associated with the Hague School, and his family connection came through his marriage to Van Gogh's cousin Ariëtte Carbentus.

Van Gogh visited Mauve in The Hague in late 1881 after returning to art with renewed determination. Mauve encouraged him to work with charcoal and pastels, then introduced him to oil painting and watercolour. Van Gogh spent several weeks working in Mauve's studio and quickly began developing the disciplined observation that shaped his early Dutch works.

Mauve's support did not last. Their relationship deteriorated in 1882, partly amid disagreements over Van Gogh's personal life and artistic choices. The common mix-up is to call Mauve simply Van Gogh's cousin: more precisely, he was a cousin by marriage. Artists such as Jean-François Millet influenced Van Gogh, but they were not his family instructor.