In interviews, many of his friends rejected the notion that he was a playboy or a poor student, and they described him as exceedingly generous. He is quick to pick up a bar tab, they said, and he liberally handed out tickets for the 2008 Beijing Olympics. “His concern for China and its people is deep-rooted and real,” said one friend in China who spends time with him during his frequent visits home. “He’s a big thinker. When he gets drunk, he talks about important things.”

While adept at throwing memorable parties, Mr. Bo was struggling with his coursework. After the union campaign, his professors forced him to take a set of exams known as “penal collections.” He failed, several students said, and was suspended for a year. Barred from using campus facilities, he moved into the Randolph, a Victorian Gothic hotel where he continued to hold parties, though a friend said they were more subdued.

His family was not pleased. Using their connections, they reportedly sent a group of emissaries, including the Chinese ambassador, to plead Mr. Bo’s case to the master of Balliol, one faculty member said. Expulsion, it was explained, would cause his family grave embarrassment.