kingpin (noun) – the most important person or thing
Here are some examples of how you can use it:
You may think our CEO is the kingpin in our company, but actually the secretary takes care of most issues.
The police won’t be able to curb (= limit) drug trafficking before they arrest Big Sniff, the kingpin of the smuggling gang.
The singer Bobby Sweet is probably the kingpin in the famous boy band.
The idea that people usually fail to evaluate the appropriate data must be the kingpin in Daniel Kahneman’s “Thinking, fast and slow.”