Robert Mugabe has been president of Zimbabwe since 1987. That is, 30 years.
And initially he was a very good leader. But lately, if you listen to his speeches, he is downright senile. And he can hardly walk on his own. That's why the general convention of serving a maximum of 2 or 3 terms is so important.
https://en.wikipedia.org/wiki/Robert_Mugabe#Prime_Minister_o...
Largely to me it seems he started with genuinely 'good intentions' that didn't work out, vs being a 'good leader'. Good to me includes both vision and execution.