Yee Jee Tso as Chang Lee (from Enemy Within).

Chang Lee is a fictional character played by Yee Jee Tso in 1996 television movie Doctor Who, , known informally as Enemy Within, a continuation of the long_running British science fiction television series Doctor Who. A Chinese street kid from 1999 San Francisco, he was an unwitting pawn of the renegade Time Lord known as the Master during the events of the movie.

When the Seventh Doctor landed on December 30, 1999 in Doctor, Lee accompanied him to the hospital carrying his effects, including a key. Told that the Doctor had died on the operating table, Lee decided to find out what the key opened, and discovered the dimensionally transcendental interior of the Doctor's TARDIS. The Master, who had taken possession of the ambulance driver's body, entered the TARDIS at the same time, convincing Lee that the Doctor was the evil one and that the TARDIS was actually his.

The Master used Lee's human retinal pattern to open the security locks that guarded the dimensional link to the Eye of Harmony, in an attempt to use it to steal the Doctor's regenerations for his own. The Doctor, in the meantime, had regenerated into his eighth incarnation and together with Dr. Grace Holloway was racing to stop the Master.

Lee was not evil, merely misled. When he found out that the Master had lied to him, he switched sides and tried to aid the Doctor instead. At the end of the movie, the Doctor thanked Lee by allowing him to keep the bags of gold dust the Master had given him from the TARDIS stores, and cryptically forewarned him to be outside of San Francisco "next Christmas". Although some fans consider him as one of the Doctor's companions, most lists omit him, as he was playing the companion role to the Master most of the time.

Chang Lee's life after his encounter with the Doctor has not been explored. Yee Jee Tso has also performed in the Big Finish Productions audio play and webcast Real Time, alongside the Sixth Doctor and Evelyn Smythe, but playing a different character.