fanatical
adj.adj. having an extreme and sometimes dangerous level of interest or enthusiasm for something. You use this to describe someone who cares about a topic or hobby much more than a normal person would.
adj. characterised by excessive enthusiasm or uncritical devotion to a cause, hobby, or belief system. Often carries a negative connotation of irrationality or obsession.
He is a fanatical supporter of the local football team.
Her fanatical attention to detail made her a great editor, but it also made her very difficult to work with.
The movement was driven by a fanatical commitment to its founding principles, often ignoring practical realities in favor of ideological purity.
Can be used both attributively before a noun and predicatively after a linking verb like 'be' or 'become'.