The Doctor regenerated six times on screen during the original Doctor Who television series from 1963 to 1989. These changes carried the programme from the First Doctor, played by William Hartnell, to the Seventh Doctor, played by Sylvester McCoy.
The six classic-series regenerations occurred in “The Tenth Planet” from the First to the Second Doctor; “The War Games” from the Second to the Third; “Planet of the Spiders” from the Third to the Fourth; “Logopolis” from the Fourth to the Fifth; “The Caves of Androzani” from the Fifth to the Sixth; and “Time and the Rani” from the Sixth to the Seventh.
The number can be confusing because regeneration is sometimes counted across the Doctor’s entire televised history rather than within the 1963–1989 run. The later 1996 television film shows the Seventh Doctor becoming the Eighth, which is outside the original series period. Other unusual transformations, such as the War Doctor and the Meta-Crisis Doctor, belong to later continuity and do not change the classic-series total.