Mr. Dimsdale was Jimmy Bond's roommate at St. Jude's Hospital in Bellingham, Washington. After Jimmy broke his leg, he was alone only briefly in the crowded hospital and soon had Mr. Dimsdale as a roommate.
Dimsdale was a cranky old man who would make wise cracks at Bond through the curtain about Bond's intelligence and so forth. Eventually he pissed off Jimmy Bond so much that Jimmy tried to get out of bed to fight the unknown man behind the curtain. This just led to Jimmy hurting himself a bit as the old man stood over him sneering cruelly.
From this point onward the curtain was gone and Jimmy interacted with the old Mr. Dimsdale a lot more. A visit by Dimsdale's son was rebuked as it became clear how much Dimsdale hated his son.Despite the animosity between Jimmy Bond and Dimsdale, Bond wanted to protect him from Dr. Bromberg, who he believed was planning on killing Dimsdale when he went under the knife. After Jimmy's accusation that fell apart and ended with him falling and severely re-injuring his leg, he encountered Dimsdale again on the way to his surgery. He told Dimsdale that he was acting like a jerk out of fear of dying alone and that he should talk with his son. At this point, he learned that Dimsdale hated his son for being a stock broker, the kind of scumbag who stuck it to the little guy. As a lifelong union man, Dimsdale couldn't stand it but Jimmy reminded the old man that he clearly didn't want to die alone though.
At the end, Dimsdale leaves the hospital on good terms with his son and Jimmy Bond.
"Take care of yourself, you big dope."