Marcel Honoree Nestor (ridder) Neels (30 December 1922 – 6 November 2016), known as Marc Sleen, was a Belgian comics artist.

During the Second World War he was imprisoned by Nazi soldiers in Fort Breendonk because his brother worked for the resistance.

[2] In October 1947, Marc Sleen started a new series, The adventures of detective Van Zwam in the newspaper De Nieuwe Gids.

Among the most well known were Piet Fluwijn en Bolleke (1947–1965), Doris Dobbel (1950–1965), Oktaaf Keunink (1952–1965) and De Lustige Kapoentjes.

[5] Sleen designed album covers for records by Flemish actor, comedian and singer Jef Burm.

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".

[2] Marc Sleen is commonly considered one of the big names of the Flemish comics, together with Willy Vandersteen and Jef Nys.

[11] On 1 January 2030, all comic characters by Marc Sleen will officially enter public domain.

An exclusive museum opposite the Belgian Centre for Comic Strip Art is devoted to his work [1].