His personality changed. He turned into a big bully.

他性格变了，成了一个大坏蛋。

《柯林斯英汉双解大词典》

At the first trial in 1998, expert witnesses dismissed her lawyers' claims that surgery for a brain tumour had changed her personality.

在1998年的最初审判中，律师声称她的性格曾因脑肿瘤手术而改变，当时专家证人摈弃此说。

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"As soon as we let him put on a dress, his personality changed from a very sad kid who sat still, didn't do much of anything to a very happy little girl who was thrilled to be alive, " Pauline said.

宝琳说：“他的性格非常忧郁，（常常）安静地坐着，什么都不做，我们一让他穿上裙子，他就变成了一个非常开心的小女孩，充满生气。”

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I've not changed my personality, and it has not stopped me in progressing in my career.

BBC: Are women their own worst enemy when it comes to the top jobs?

What if it turned out that by enhancing intellectual ability, some other personality trait changed as well?

CNN: ASIANOW - TIME Asia | Brainteaser

Tommy said his personality also changed following the stroke.

BBC: NEWS | Health | Creative side unlocked by stroke