Marcellus is believed to have been born in the village of Nievern an der Lahn, five miles [seven kilometers] southeast of Koblenz, in Germany.
The first known mention of Marcellus was in 1426, when he was arrested in Lübeck for selling forged letters of mortgage and subsequently escaped from prison.
Then, with the help of his new friend, he pretended to be a Knight of St. John throughout northern Germany to collect the money for ransoming the King of Cyprus from Turkish captivity.
The conditions of his cell were so bad that he wrote and sent letters, which have been preserved, to the officers of the Prince-Archbishop to beg for his freedom.
He quickly gained the trust of the King again and presented letters to show that he had been greatly disrespected and mistreated.
After a great deal of conflict and political maneuvering, the dispute ended in the summer of 1454, when Kalteisen resigned and went south to Rome.
On his way back to Copenhagen, he was attacked, robbed and imprisoned in Cologne, perhaps with the encouragement from the Papal authorities, but he managed to get himself released from the prison.
[4] To avenge the mistreatment of his friend, Christian I confiscated all the assets of the Archbisophric's people who were living and visiting within his kingdom.
With the titles of the King's Chancellor, the Royal Councilor and the Bishop of Skálholt, he was one of the most powerful and influential men in Denmark and indeed all of Scandinavia.
[6] He was able to win most of the Icelandic höfðingjar [chieftains] over to his side but he is known to have banned the priest-poet, Jón "Maríuskáld [Mary's Poet]" Pálsson, but the reasons are not known.
To oversee his diocese in Iceland, Marcellus had Andrew, already the Bishop of Garðar in nearby Greenland, appointed as the Vice-Bishop (or Vicar) of Skálholt.
But, for commercial and financial matters in Iceland, Marcellus had two other assistants, Bjorn Thorleifsson and Daniel Kepken, who were as unscrupulous as he was.
1462 is the more likely year because in October 1462 King Christian recognized the election of Jón Stefánsson Krabbe, a Dane, as the new Bishop of Skálholt.