First off, nothing lives in an active volcano unless it is an extremely magical thing.
However an extinct volcano would make a good place for a dragon to live as:
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Dragons are often associated with volcanoes because of their powerful and fiery nature, which aligns with the image of volcanic activity. The idea of dragons living in volcanoes adds to their mystique and portrays them as beings of immense power and danger. Additionally, the heat and harsh conditions of a volcano may be seen as a suitable environment for a creature as strong and resilient as a dragon.
Some people live by volcanoes due to the fertile soil and land that is good for agriculture. Others may live near volcanoes for cultural or historical reasons. Additionally, some people may not have the means to relocate to safer areas.
Farmers mostly live near volcanoes.They live near volcanoes because of the good fertilizer which makes good crops.
in the ocean
Never.
Well you wouldn't want to live near a volcano would you? Its quite obvious volcanoes erupt hot lava/magma which burns everything in its path, including people. People do live near volcanoes though, but they live near dormant or extinct volcanoes and have warnings before erruptions and are usually able to escape if they keep calm. Back to why you shouldn't live near them. The areas around volcanoes have a more likely chance of an earthquake. Also the areas around volcanoes that have erupted before is often "black" and bare. Volcanoes release poisonous gases too.