carlos ghosnFormer Renault-Nissan-Mitsubishi head Carlos Ghosn.Keith Tsuji/Getty

Last week, the auto industry was rocked to its core when legendary executive Carlos Ghosn was arrested in Japan.

Ghosn, 64, was chairman and CEO of Renault, chairman of Nissan, chairman of Mitsubishi, and the architect of a tripartite alliance that in 2017 was the world’s biggest automaker by sales.

Ghosn was a celebrity CEO, a Brazilian-born leader of Lebanese descent who came of age in France. In the early 2000s, Ghosn took charge at the newly formed Renault-Nissan alliance and steered the two automakers toward revival and global dominance, competing in numerous markets and challenging General Motors, Toyota, and Volkswagen.

He was feted in Japan, where, as an outsider, he broke into that country’s insular auto industry. As with the late Fiat Chrysler Automobiles CEO Sergio Marchionne, his every utterance was closely followed on the worldwide car circuit. He was wildly successful, risk-taking, borderline arrogant and at-times despotic, but also considered incredibly wise.

Following his arrest, Nissan revealed that it has passed along a whistleblower tip to the Japanese authorities, leading to allegations that Ghosn had been detained in Japan due to financial misdeeds and fraud. Auto executives have fallen before, but none were as big as Ghosn, and none had enjoyed such long careers at the top.

Lacking official charges — Japan can hold Ghosn for 20 days before any sort of indictment — plenty of theories have developed about what he actually did or didn’t do. Here’s a roundup: