Single Word Request - What do you call a person who can drink a lot?

Solution 1:

Most of the words that come to mind are archaic, which I don't think it what you're looking for. Interestingly, in Benjamin Franklin's time, you could have said someone was "biggy," which I could see coming back into use. Other things you could call your drinker would be soak or toper. I can't think of any modern word that doesn't also mean alcoholic, however. Here's Franklin's list of related words: https://founders.archives.gov/documents/Franklin/01-02-02-0029

Solution 2:

People, who can't hold their alcohol well, are called lightweight.

The antonym and the word, which you are looking for, is a heavyweight.

Obviously, these two words are slang and not very formal.