In the speech, lewis referred to a "great father" and "great chief'. who was this?

The answer is Thomas Jefferson

Explanation:

During interactions with indigenous peoples, Great Father was the title used by the colonial powers in North America during the 19th century to refer to the President of the United States, the Monarch of Canada (It was also possible to refer to the British monarchs King George III and Queen Victoria as "the Great Father" and "the Great White Mother"), the King of Spain or the King of France.