Fitz is from the Anglo-Norman fitz (son of) — a prefix in Norman surnames. Fitzgerald "Fitz" Grant III — male character on ABC's Scandal (2012-2018), played by Tony Goldwyn; the fictional Republican US President; Scandal was the first network drama to feature an African American female lead (Kerry Washington as Olivia Pope) in nearly 40 years; created by Shonda Rhimes; ran for 7 seasons across 124 episodes. F. Fitz Fitzgerald — modern American figure.
Fitz does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
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In Pythagorean numerology the letters of Fitz reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.