Peace Offensive") (1951), Nero visits Joseph Stalin to make him drink an elixir that will make him a pacifist. Besides Nero Sleen drew many other comic strip series, many of them gag-a-day comics, for magazines like 't Kapoentje and Ons Volkske. Among the most well known were Piet Fluwijn en Bolleke (1947–1965), Doris Dobbel (1950–1965), Oktaaf Keunink (1952–1965) and De Lustige Kapoentjes. Sleen also drew a daily cartoon during the Tour de France from 1947 until 1965, called De Ronde van Frankrijk. Between 1950 and 1965 Sleen published Nero in Het Volk, after which he moved to De Standaard. This caused a huge copyright controversy, as several newspapers fought over the rights over his syndicated comics. Thousands of readers switched from Het Volk to De Standaard, just to follow his adventures in the newspaper. After that switch, he dropped all other series and devoted himself solely to Nero. From 1992 to 2002, he was aided by Dirk Stallaert, a young Flemish comic artist, and at first the intention was to let Stallaert continue the series after Marc Sleen retired. But in the end, Stallaert didn't feel ready to continue it alone, and at the end of 2002, at the age of 80, Marc Sleen ended his career as a comics artist. Sleen designed album covers for records by Flemish actor, comedian and singer Jef Burm. Burm was a former school mate of his. TV documentary work Marc Sleen was also known as a traveller and animal friend. He made 35 safaris to Africa between 1961 and 1991, making more than 20 documentaries for the Vlaamse Radio- en Televisieomroep, mostly for the TV show "Allemaal Beestjes". A few books and records about his safaris appeared as well. Many of his comics featured animals and countries he has visited. Legacy Marc Sleen is commonly considered one of the big names of the Flemish comics, together with Willy Vandersteen and Jef Nys. In 2005 he was selected as one of the 111 nominees for the title "The Greatest Belgian" (De Grootste Belg) in the Flemish edition. He ended in 48th place. On 19 June 2009, a museum dedicated to his life and career was opened in Brussels: the Marc Sleen Museum. Both Marc Sleen as well as King Albert II of Belgium were present. The king was a fan of Nero since his youth and both he and Baudouin of Belgium learned Dutch