Mother Theresa is famous for her charity.
✗ Mother Theresa is infamous for her charity.
Hitler is infamous for his evil deeds.
✗ Hitler is famous for his evil deeds.
"Famous" simply means "well-known".
What is she famous for?
She is well-known. I'm asking what she has done to become well-known.
"Infamous" means to be well-known for something negative.
The murderer became infamous when covered on national news.
Many people know of the murderer for committing terrible acts.
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