Paul Ehrlich wani likitan Jamus ne kuma masanin kimiyya wanda ya rayu daga 1854 zuwa 1915. An fi saninsa da aikinsa a fannin rigakafi da haɓaka tunaninsa na "harsashin sihiri" a matsayin maganin da aka yi niyya don cututtuka. An ba shi lambar yabo ta Nobel a fannin Physiology ko Medicine a 1908 saboda gudummawar da ya bayar wajen fahimtar rigakafi. Kalmar "harsashi mai sihiri" tana nufin ra'ayin cewa za'a iya samar da magani wanda zai zaɓa da kuma lalata wani takamaiman abin da ke haifar da cututtuka ba tare da cutar da kyallen jikin majiyyaci ba. Ayyukan Ehrlich sun kafa harsashin haɓaka ilimin chemotherapy da sauran hanyoyin kwantar da hankali.