*Cough ahem* Pedant alert. He didn't train Darth Vader (or Anakin). He recommended that he be trained to the Jedi Council. He was killed before any training actually took place - he only returned to the Jedi fold after Anakin turned to Vader to instruct Yoda and Obi Wan how to live on after death.
*pre-emptive celebratory nipple tassle jiggle* - Sean Ewington