Given the question: What was the last name of Drake's mentor?  Answer the above question based on the context below:  Although the publicity generated by Five Leaves Left was minor, Boyd was keen to build on what momentum there was. Drake's second album, 1971's Bryter Layter, again produced by Boyd and engineered by John Wood, introduced a more upbeat, jazzier sound.Disappointed by his debut's poor commercial performance, Drake sought to move away from his pastoral sound, and agreed to Boyd's suggestions to include bass and drum tracks. "It was more of a pop sound, I suppose," Boyd later said. "I imagined it as more commercial." Like its predecessor, the album featured musicians from Fairport Convention, as well as contributions from John Cale on two songs: "Northern Sky" and "Fly". Trevor Dann noted that while sections of "Northern Sky" sound more characteristic of Cale, the song was the closest Drake came to a release with chart potential. Cale used heroin during this period, and his older friend Brian Wells suspected that Drake was also using.Boyd and Wood were confident that Bryter Layter would be a success, but it sold fewer than 3,000 copies. Reviews were again mixed: while Record Mirror praised Drake as a "beautiful guitarist—clean and with perfect timing, [and] accompanied by soft, beautiful arrangements", Melody Maker described the album as "an awkward mix of folk and cocktail jazz".Soon after its release, Boyd sold Witchseason to Island Records, and moved to Los Angeles to work with Warner Brothers to develop film soundtracks. The loss of his mentor, coupled with the album's poor sales, led Drake into further depression. His attitude to London had changed: he was unhappy living alone, and visibly nervous and uncomfortable performing at a series of concerts in early 1970. In June, Drake gave one of his final live appearances at Ewell Technical College, Surrey. Ralph McTell, who also performed that night, remembered: "Nick was monosyllabic. At that particular gig he was very shy. He did the first set and something awful must have happened. He was doing his song 'Fruit Tree' and walked off halfway through it."In 1971,...
The answer is:
Boyd