Claudius Clavus (Suartho) also known as Nicholas Niger -
- (Danish: Claudius Claussøn Swart), (born 14 September 1388) -
- was a Danish geographer -
- sometimes considered to be the first Nordic cartographer.

It is believed that he was born in the village of Salling -
- on the Danish island of Funen.
He is commemorated by a plaque in the local Aagaarden.

In 1412–13 at the age of 25 he started to travel around Europe -
- and appeared eleven years later (1423–24) in Rome.
It is believed he travelled as far north as the 70°10' N. lat. 
In Rome he became friends with the cardinal Giordano Orsini - 
- and the pope's secretary Gian Francesco Poggio Bracciolini -
- who were among those working to update -
- the old Roman cartography.
Claudius contributed to a more realistic description
- of Nordic countries, in particular Iceland and Greenland -
- and was probably the first cartographer to put Greenland on a map.
He is also known for having named Greenlandic places -
- by using lyrics from old folk songs.

Most of his work (including two maps) is lost -
- but a copy has been preserved through the German cartographers -
 - Donnus Nicholas Germanus and Henricus Martellus Germanus -
- and in the nineteenth century more texts were rediscovered -
- in the imperial library at Vienna.
He drew 27 maps for a copy of the Geography by Ptolemy.