Peter Jones was the only original Dragon's Den investor to remain on the panel continuously from the programme's launch.
Jones joined the original British panel when the series began in 2005. Over the years, other original dragons left and were replaced, while Jones continued to appear as a regular investor. His long tenure made him one of the most recognisable figures associated with the programme.
The original panel included Jones alongside Duncan Bannatyne, Rachel Elnaugh, Doug Richard and Simon Woodroffe. Theo Paphitis was also an early and prominent dragon, which is why he is sometimes incorrectly named in this question.
The distinction is between being an original panellist and appearing continuously. Several investors were important to the early series, but only Jones held that uninterrupted panel position.