Doctor Who: 8 Reasons The Tenth Doctor Was An Actual Monster
2. He Became The Time Lord Victorious
Towards the end of his life, the Tenth Doctor decided that the rules of time were his to break. As the last of the Time Lords, there was nobody to stop him, and instead of letting people die, he could save them. It began with the events of Bowie Base One when he decided to rescue Captain Adelaide Brooke and others, who should have rightfully died there.
Adelaide made her feelings known about the Doctor's decision to change history after he spent so long telling her why he couldn't. He brushes off all the criticism, and the conversation sadly ends with Brooke's suicide.
Ten had always been pompous and arrogant, but when he decides to take on the Time Lord Victorious persona, it's like nothing we've ever seen. He becomes reckless and sincerely believes he can do whatever he wants.
While this time period was only glimpsed in TV canon, the recent Time Lord Victorious event delved much deeper into this time when Ten was at his darkest and explored his adventures across all kinds of media: books, comics, audios, etc.