The martyrs died for their christian belief.
There are hundreds of martyrs who died in a number of gruesome and grisly ways. A more specific answer requires a more specific question.
If you mean John the Baptist then yes. If you mean John the apostle, then no, as it is believed he was alone among the disciples in dying a natural death.
St. George was tortured and beheaded about the year 304 at Lydda, Palestine
St. Francis of Assisi did not die a martyr's death. He died of natural causes.