Original: Considered by many as a founder or precursor of 20th-century existentialism , his Notes from Underground ( 1864 ) , written in the embittered voice of the anonymous '' underground man '' , was called by Walter Kaufmann the '' best overture for existentialism ever written .
Simplified: He is sometimes considered to be a founder of existentialism , most frequently for Notes from Underground , which has been described by Walter Kaufmann as the best overture for existentialism ever written .