Samuel Clemens first adopted the pen name 'Mark Twain' in 1863.
Notes on verification
Corroborated by multiple reputable, independent sources including the Mark Twain House & Museum, Encyclopedia Britannica, and PBS, consistent with established Twain scholarship. [cascade flags: aggregator_dropped_primary_exists | tier=silver indep_score=0.875 clusters=2 claim_tier=everyday | framework convergence=partial (upstreams: Mark Twain Papers and Project (UC Berkeley), Mark Twain House & Museum archives) — publishers independent, evidence may not be | kind=empirical eligibility=high]
Sources
- Unswerving irregularity | USPTO (seed:firsts_and_inventions)
- https://www.marktwainhouse.org/about/mark-twain/mark-twain-biography/ (corroboration)
- https://www.pbs.org/marktwain/l_mt/l_mt_pseudonym.html (corroboration)