Oswald Achenbach (1827–1905) was one of Germany’s most significant 19th-century landscape painters and a key figure in the Düsseldorf School of painting, alongside his older brother, Andreas Achenbach. The two brothers were often humorously referred to as the “Alpha and Omega of landscape painting” by their contemporaries. Born in Düsseldorf, Oswald showed an early interest in art, following his brother to the Düsseldorf Academy at just eight years old, despite the official entry age being twelve. However, dissatisfied with the academy’s teachings, he left after six years and joined two local artist groups: the *Verein der Düsseldorfer Künstler zur gegenseitigen Unterstützung und Hilfe* (Düsseldorf Artists’ Association) and the *Malkasten*. His first travels abroad were in 1845, to Italy and Switzerland, followed by longer stays in southern France and Italy in 1850. From the beginning of his career, Oswald was often compared to his highly successful brother Andreas. To avoid direct competition, the brothers divided their painting subjects geographically, with Oswald focusing on southern landscapes, particularly Italian scenes, and Andreas specializing in northern European views. Oswald’s favorite subjects included views of Vesuvius and the Naples area, often depicted at night, where he concentrated on capturing the effects of light and shadow in a calm, atmospheric style. In contrast, Andreas was known for his dramatic seascapes and depictions of rough, turbulent moments. Both brothers achieved international fame early in their careers, with Oswald becoming an honorary member of several prestigious academies, including those in Amsterdam, St. Petersburg, and Rotterdam. He was awarded a prize at the 1855 Exposition Universelle in Paris and received honors from both Napoleon III and Maximilian of Mexico. In 1863, Oswald was appointed a professor of landscape painting at the Düsseldorf Academy, and in 1897, he was made an honorary citizen of Düsseldorf. His home became a cultural hub, frequented by artists, intellectuals, and members of the nobility. Oswald Achenbach remained in Düsseldorf until his death in 1905, leaving behind a legacy of around 2,000 paintings. In recent years, the works of both Achenbach brothers have been rediscovered in the art market. A notable sale occurred in 2017, when *Summer Evening in the Bay of Naples* was sold for €204,000, setting a world record for a painting by Oswald Achenbach. The *Malkasten* in Düsseldorf continues to hold regular information days showcasing their works.