Examples:
xxx was the founder of …
xxx was the first …
This does not limit to living person/person passed away, but also items.
To me the status of the first, the founder of etc. does not change and stays there forever. Its always true.
Something that changes e.g. yyy was the fastest computer makes more sense as the fastest can be replaced with something more modern.
Best Answer
The past tense is used because the events involved were in the past.
is grammatically correct because he was king in the past, even though the statement will always be true.
However,
is also grammatically correct, because the event of her becoming President is in the future. After her presidency had ended, it would become "Hilary Clinton was the first female President". So "Barack Obama is the first African-American president."