A ruler/king/president/minister who has an uncontrollable amount of power and uses it abusively and is unrestrained by the law or constitution.
1)Taken From the Pink Floyd Song: The Fletcher Memorial Home
"Ladies and Gentlemen, please welcome Reagan and Haig
Mr. Begin and friend Mrs. Thatcher and Paisley
Mr. Brezhnev and party
the ghost of Mccarthy
the memories of Nixon
and now adding colour a group of anonymous latin
american meat packing glitterati"
2) Person 1: Bush was a real tyrant, man!
Person 2: Totally dude, just like that Hilter guy.