Oskar Artur Alexander (Zagreb, 1876 – Samobor, 1953) was a Croatian academic painter and professor. He came from a prominent Jewish family in Zagreb, and his work links the painting of the Austro-Hungarian monarchy with early twentieth-century Croatian art.
He trained from 1894 to 1899 at the Academy of Fine Arts in Vienna, under Franz Rumpler and Franz von Matsch, and then at the Académie Julian in Paris, under Eugène Carrière and James Abbott McNeill Whistler. In Paris he painted Émile Zola in a café and also portrayed Oscar Wilde. He exhibited in Paris and Munich in 1900, and from 1908 was an active member of the Hagenbund. Together with Vlaho Bukovac and Viktor Kovačić he co-founded the Association of Croatian Artists.
In 1912 the provincial government of the Kingdom of Croatia-Slavonia named him professor of fine arts. During the First World War he worked as a war painter, sketching compositions on the battlefield and later transferring them to canvas, for which he received a medal from Franz Joseph I. He also portrayed Engelbert Dollfuss, Vladko Maček and Josip Broz Tito.
He died in Samobor in 1953, marked by the Holocaust, which he barely survived, and by the events of the Second World War.