Sepp is a given name. When borne by Upper German-speaking people, it is often a nickname for Josef or other names related to Joseph.
Those bearing it include:
Joseph Sepp Blatter (born 1936), disgraced suspended president of FIFA
Josef Bradl (1918-1982), Austria ski jumper and coach
Sepp Daxenberger (1962–2010), Bavarian politician
Sepp De Roover (born 1984), Belgian footballer
Josef Sepp Dietrich (1892–1966), World War II Oberst-Gruppenführer of the Waffen-SS
Sepp Ferstl (born 1954), German alpine skier
Josef Sepp Herberger (1897–1977), German football player and manager
Josef Hirtreiter (1909-1978), German SS sergeant and Holocaust war criminal
Sepp Holzer (born 1942), Austrian permaculturalist and consultant for natural agriculture
Josef Hügi (1930-1995), Swiss footballer
Sepp Kerschbaumer (1913–1964), Italian terrorist
Sepp Kusstatscher (born 1947), Italian politician
Josef Sepp Maier (born 1944), German goalkeeper
Josef Oberhauser (1915–1979), German Nazi SS officer
Josef Sepp Piontek (born 1940), German former football player and manager
Sepp Schönmetzler (born 1944), German figure skater, coach and journalist
Sepp Straffner (1875–1952), Austrian federal railway official and politician
Josef Uhlmann (1902–1968), German fencer, participated at the 1936 Summer Olympics
Sepp Walcher (1954–1984), Austrian alpine skier
Sepp Weiler (1921–1997), German ski jumper
Sepp Weiß (born 1952), German former footballer
Josef Wurmheller (1917–1944), German Luftwaffe ace
Josef Sepp Zeilbauer (born 1952), Austrian retired decathlete