What do you mean by “hot under collar” and “Der Fuhrer”?

In Jesse Owen’s autobiographical writing “My Greatest Olympic Prize”, the expression “hot under collar” means ‘angry’ and ‘Der Fuhrer‘ means ‘leader’, referring to Adolf Hitler.
 
The author says that he was angry when he came to know about Hitler’s trickery to win the Board Jump event and determined to show the leader and his race who was superior and who was not.

“Hot under collar” means ANGRY and “Der Fuhrer” means LEADER.