Complex sentence: Nafissatou "Nafi" Thiam (born 19 August 1994) is a Belgian Walloon athlete who became Olympic champion in the heptathlon at the 2016 Summer Olympics and world champion in the same discipline at the 2017 World Championships.
Split into simpler sentences: Nafissatou "Nafi" Thiam (born 19 August 1994) is a Belgian Walloon athlete. She won the gold medal in the heptathlon at both the 2016 Summer Olympics and the 2017 World Championships.