There are many that have died for their belief in God.
There are hundreds, if not thousands, of Christian martyrs so you need to narrow your question a bit.
Stephen 26th December
St. Stephens Day is the Christian festival (feast) that commemorates St. Stephen, who by Christian tradition was the first Christian to be martyred for his faith.(Book of Acts chapters 6, 7 & 8)It is 26 December, the day after Christmas Day.The Feast of St. Stephen the First Martyr is December 26.
June 1st is the feast day of St. Justin the Martyr.
Saint Rebecca the Martyr's feast day is September 4.March 23 is St. Rebecca's feast day.
August 10 is the feast of St. Lawrence, deacon and martyr.
The Feast of Stephen, deacon and martyr, is always on December 26.
The feast of St. Lawrence of Rome, deacon and martyr, is August 10.
Valentine's Day is the feast day of St. Valentine of Rome, a priest and martyr in the early Church.
A number of saints share December 26 as a feast day but the best known is Saint Stephen, Deacon and Martyr.
December 26 is the feast of St. Stephen, deacon and martyr.
Abassad was a bishop and martyr of the early Christian church. After being tortured in a variety of ways, he was beheaded by the command of Arrianus under Diocletian. His feast day is December 23.
St. Stephen is the protomartyr, the first martyr in the new Church so his feast day falls the first day after Christmas.