James Blackadder was Roland Mitchell's thesis supervisor, and now he's Roland's employer. Scottish, "stringent" (2.3), and just a teensy bit curmudgeonly, Professor Blackadder is the kind of scholar who spends his life chipping away at a plain and practical project—in his case, an annotated edition of Randolph Henry Ash's Complete Poems and Plays (2.15). He doesn't have any of Mortimer Cropper's scholarly fame and pizzazz, but—fortunately for the novel's heroes—he lacks Cropper's greed and self-importance, too.
Blackadder has been working on Randolph Henry Ash's writings for so long that he sometimes finds it difficult to distinguish his own thoughts and ideas from Ash's. Every now and then, it makes him anxious to think "that he would end his working life, that is to say his conscious thinking life, in this task, that all his thoughts would have been another man's thoughts, all his work another man's work" (2.18). Luckily for him, he's really and truly fascinated by Ash's writings, which makes him inclined to accept his "subordination" (2.18).
For Roland Mitchell, writing his doctoral thesis under Blackadder's supervision was "a discouraging experience" (2.3). As Possession's narrator tells us,"Blackadder was discouraged and liked to discourage others" (2.3). Whereas Mortimer Cropper funds his Randolph Henry Ash research with a bottomless bank account, Blackadder toils away with minimal funding in the basement of the British Museum. What's worse, Blackadder's research facilities are funded in part through his rival's "goodwill"—a situation he expects Cropper to use to his own advantage someday.
Luckily for Blackadder, things are looking up by the end of Possession. The discovery of the Ash-LaMotte correspondence inspires a large endowment of research funds that he'll be able to use to his benefit, and his blossoming friendship with Leonora Stern is helping to make him a more daring, adventurous, and lighthearted man. That's a win-win for everyone.