Marcus Roy was born in 1577 at Sigmaringen in the County of Hohenzollern-Sigmaringen (modern southern Germany) to a noble Hohenzollern-Sigmaringen family. Educated at the University of Freiburg im Breisgau, Marcus received the Doctor of Civil and Canon Law and became famous during his youth as the 'Advocate of the Poor' (Latin *Advocatus Pauperum*) — the lawyer who systematically defended the poor without payment.
In 1612, at the age of 35, Marcus entered the Capuchin Order — taking the religious name Fidelis ('Faithful') — the young-adult conversion from professional legal career to Capuchin religious life that established his conversion pattern.
Fidelis undertook the Capuchin preaching ministry across southern Germany, Austria, and Switzerland — becoming the famous Capuchin preacher of the Counter-Reformation era.
In 1621, the Sacred Congregation of Propaganda Fide — the new Vatican Congregation for the Catholic missions, established by Pope Gregory XV — sent Fidelis as Prefect of the Capuchin mission to the Calvinist Grisons region of Switzerland (modern Canton of Graubünden).
On April 24, 1622, after preaching the Catholic Real Presence doctrine at the village of Seewis im Prättigau, Fidelis was attacked by a Calvinist Grisons mob who hacked him to death with cudgels and knives — the protomartyr of the Congregation for the Propagation of the Faith.
Canonized on June 29, 1746 by Pope Benedict XIV.