This is the 4050th most frequent Polish word.
zełenskiego
"Zełenskiego" is the genitive case of "Zełenski," typically referring to something belonging to or associated with Zełenski, a name (e.g., Volodymyr Zelensky, the Ukrainian president).
In this sentence, "Zełenskim" is used in the instrumental case to indicate interaction with a person.
Spotkałem się z prezydentem Ukrainy, Wołodymyrem Zełenskim.
I met with the President of Ukraine, Volodymyr Zelensky.
Here, "Zełenskiego" is in the genitive case denoting possession or origin.
List od Zełenskiego przyszedł do nas wczoraj.
A letter from Zelensky arrived to us yesterday.
In this context, "Zełenskiego" is in the genitive case to signify relation or reference to an individual's speeches.