India, June 1 -- Fans of Doctor Who got a massive surprise in the series finale when Ncuti Gatwa's Doctor regenerated into Billie Piper. That's right: the beloved actress, best known to Whovians as Rose Tyler, stepped back into the TARDIS "one more time". But who exactly is Rose Tyler, and why does her return matter so much?

Rose Tyler, introduced in 2005 when the show relaunched after a long hiatus, was the first companion of the modern Doctor Who era.

Billie Piper starred alongside Christopher Eccleston's Ninth Doctor and later David Tennant's Tenth, and quickly became a fan favourite. Her character was an ordinary shop girl from London who became special through her travels across time and space.

Piper played Rose for two full serie...