the Ringo Starr of metals

'Moriarty is the Napoleon of crime'

is a famous early example of the snowclone ['The Final Problem, Sir Arthur Conan Doyle].

'X is the Y of Z'.

Y has to be famous, and unequalled (in a good, bad, or just ... er ... unequalled way) in its class, and the assertion is that X is similarly unequalled in the domain Z.

There's only one (relevant) Napoleon, Ringo Starr.... Hence the definite article is required, the implication being that X is as unique or at least as well known in their/its field Z as Y is in the unspecified relevant field.

The snowclone (and particularly its offspring) is referred to in Wiktionary Appendix: Snowclones/X is the new Y:

[The snowclone,] in its first form, "X is the Y of Z", was said by Diana Vreeland as "pink is the navy blue of India" in the early 1960s.

This phrase was originally used with colors, and the "X is the new Y" form appeared in the 1980s with many colors being referred to as "the new black".

Of course, the Conan Doyle example is far earlier.

Other examples of the original form to be found on the internet are:

• Qatar Is the Tiger of the Middle East
• fluorine is "the tiger of chemistry"
• Chicken parm sandwich with vodka sauce is the Julius Caesar of sandwiches.
• Cripps was the Churchill of the battle for national solvency.
• Bob Hawke was the Don Bradman of Australian politics.
• Rameses, who was the Louis XIV of the Egyptian race.
• [Tsar Nicholas] ... 'the Nebuchadnezzar of the North'.