He seems to have spent most of his time fighting the Moors and driving them out of Spain.
As they were considered heathen heretics, no doubt this was considered a very Christian thing to do in those times.
Then build a few ostentatious cathedrals in captured cities and presto — you’ve won a halo.
St FERDINAND-OF-CASTILLE FACTS AND FIGURES
Name : FERDINAND-OF-CASTILLE
Pronunciation : Coming soon
Alternative names : None known
Location : Worldwide Christianity
Gender : Male
Type : saint
In charge of : Unknown at present
God of :
Celebration or Feast Day : Unknown at present
Birth and Death Dates : 1198-1252
Good/Evil Rating : Unknown at present
Popularity index : 1311