Formal:
* Erudite: This implies deep, scholarly knowledge.
* Learned: This suggests a high level of education and knowledge.
* Savant: This refers to someone with exceptional knowledge in a specific area.
* Scholar: This is someone who has a deep understanding of a particular subject.
* Expert: This indicates someone with specialized knowledge and skills.
Informal:
* Knowledgeable: This is a general term for someone who has a lot of information.
* Well-informed: This suggests that someone has a good understanding of current events and topics.
* Brilliant: This implies exceptional intelligence and insight.
* Wise: This suggests that someone has a deep understanding of life and the world.
* Astute: This implies someone with keen judgment and understanding.
More specific:
* Historian: Someone with extensive knowledge of history.
* Scientist: Someone with expert knowledge in a scientific field.
* Linguist: Someone with deep knowledge of languages.
* Philosopher: Someone with extensive knowledge of philosophy.
* Polymath: Someone with a wide range of knowledge across multiple subjects.
The best word to use will depend on the specific situation and the level of formality required.