Why would Grandpa chose these folks?
Grandpa likes Mozart but not Tchaikovsky
Grandpa likes Queen Victoria but not Mary, Queen of Scots
Grandpa likes Gandhi but not Mandela
Hmmm.
Since the answer is not
people with 8 letters in their first name,
Could Grandpa like...
Major Civilization 6 characters?
He likes
Mozart but not Tchaikovsky
He likes
Queen Victoria but not Mary, Queen of Scots
He likes
Gandhi but not Mandela
Grandpa likes
people commonly referred to with first names that is not their real first name
Mozart:
Born: Johannes Chrysostomus Wolfgangus Theophilus Mozart
Commonly called: Wolfgang Mozart
Ghandi:
Born: Mohandas Karamchand Gandhi
Commonly Called: Mahatma Gandhi
Queen Victoria:
Born: Alexandrina Victoria
Commonly Called: Victoria
Could it be
Grandpa likes those who came before.
Grandpa likes Mozart but not Tchaikovsky who was inspired by Mozart
He likes Victoria but not Mary, Queen of Scots who was her descendant
He likes Gandhi but not Mandela who was inspired by him.
Grandpa is short so he likes short people