In a 2014 discussion with his biographer Michael D’Antonio, Trump explained,

When I look at myself in the first grade and I look at myself now, I’m basically the same. The temperament is not that different.

However, he has also asserted that he had the best temperament of anyone who has ran for President.

In other discussions with his biographer, Trump noted how as a child he enjoyed fighting, which was one of the reasons he was sent to a military academy.

He has also described himself as a “whiner,” and taken shots at over Twitter at all his “haters,” even on the anniversary of 9/11.

Politico – What I Learned Writing Trump’s Biography
The Washington Post – The scariest thing I found out about Donald Trump yesterday
The Week – Donald Trump tells biographer he’s the same now as he was in first grade