Johann Kaspar Mertz, born Casparus Josephus Mertz on August 17, 1806, in Pressburg (now Bratislava, Slovakia), was a prominent Hungarian guitarist and composer of the 19th century. He was a leading virtuoso guitarist, known for his lyrical compositions. Mertz's early life was marked by poverty, and he began playing the guitar and flute as a youth, eventually giving music lessons to support himself.

Mertz's career took a significant turn when he performed in a concert organized by Johann Nepomuk Hummel in 1834. By 1840, he had moved to Vienna, where he quickly became part of the city's social and artistic elite, thanks to a successful concert at the Hofburgtheater under the patronage of Empress Carolina Augusta. His music was published by the prestigious Haslinger publishing house during this period.

In 1841, Mertz embarked on a concert tour across Austria, Poland, and Russia. He met the pianist Josephine Plantin in Dresden in 1842, and they married later that year in Prague. The couple settled in Vienna, where they were active as teachers, composers, and concert artists, often performing their compositions for guitar and piano.

Mertz's health suffered a setback in 1846 when he was diagnosed with neuralgia and nearly died from an overdose of strychnine, prescribed as a treatment. His wife nursed him back to health, and he resumed his career in 1848. Mertz's compositions, such as the Bardenklänge, Op. 13, reflected the Romantic piano styles of Chopin, Mendelssohn, Schubert, and Schumann, diverging from the classical guitar forms of Sor and Aguado.

In 1856, Mertz won a first composition prize in a Brussels guitar competition with his Concertino per Chitarra sola, although he passed away on October 14 of that year before learning of his success. Mertz's legacy includes his influence on guitar music, characterized by a blend of lyrical expression and technical demands, inspired by the Romantic era's pianistic models.