Do we know of any martyrs from among the Roman Catholic Church that lived during the five centuries before Martin Luther (i.e., 10–15th centuries)? I am especially interested in those who have been well-spoken of by Martin Luther.
St. Thomas Beckett - 1170 - assassinated at a church for annoying the king who made him Archbishop.
St. Berard and companions (of Assisi) - 1226 - killed by the Moors
Bl. Charles the Good - 1127 - killed at church after stopping black marketers
St. Stanislaus - 1079 - killed after excommunicating a wicked king.
St. Elphege - 1012 - killed by Danish invaders for refusing ransom by selling off his church property.
St Adalbert - 983 - killed evangelizing Prussians.
St. Joan of Arc - 1412 - (not canonized until 1920, but pardoned thirty years after her death) burned at the stake and not really a martyr, but I thought I'd throw her in here.
St Wenceslaus - 929 - killed by his brother while praying in a church.
St. John Nepomucene - 1390 - drowned in the Vltava by a very different King Wenceslaus for refusing to violate the Seal of confession.
I found these folks just by looking through my lives of the saints book there are undoubtably more. I haven't a clue about Luther's knowledge of these particular saints. However, I think it's safe to say that educated people knew about St Thomas Beckett and may have heard about Joan of Arc in Western Europe (From the Canterbury Tales and Joan of Arc is now the patroness of France). As in Eastern Europe they may have known of St. Wenceslaus and St Stanislaus (patrons of Czech Republic and Poland). Their cults didn't operate in a complete vacuum.