Elizabeth "Betsy" Braddock was created by Chris Claremont and Herb Trimpe. In the UK, she was first introduced in Captain Britain Vol. 1 #8 (1976), published by Marvel UK. In the United States, she was introduced in New Mutants Annual #2 (1986), where she started calling herself "Psylocke."
After that, she joined the X-Men in Uncanny X-Men #213 and became a long-standing member. However, after a trip through the Siege Perilous, Betsy was taken by the Hand and brainwashed into becoming an assassin named "Lady Mandarin" and her body was changed into that of an Asian woman. Later on, it turned out that her body was actually switched with the body of a woman named Kwannon.
Kwannon, in Betsy's body, started calling herself "Revanche" and originally claimed that Betsy was an imposter, before the entire situation was cleared up. Kwannon, however, ended up dying of the Legacy Virus, meaning that Betsy was stuck in her body.
Until, that is, Hunt for Wolverine: Mystery in Madripoor. After having her life essence drained by the mysterious villain Sapphire Styx, Betsy used her considering psychic abilities to reconstruct a body for herself based on her original body. And Kwannon's body, it turned out, was inhabited again by Kwannon, undoing the bodyswap after 29 years.
After the Soft Reboot House of X and Powers of X, Betsy became the lead of Excalibur (2019) and took on the role of Captain Britain, while Kwannon decided to take name Psylocke and used it as the leader of the Fallen Angels and the Hellions.