This is the 17516th most frequent Polish word.
założycieli
"Założycieli" means "founders" in English.
The word "założycielami" is in instrumental plural form indicating the people referred to as 'founders' who are interacted with in this context.
Spotkałem się z założycielami tej organizacji.
I met with the founders of this organization.
The word "założycieli" is in genitive plural form showing possession or association to the 'founders'.
Nazwiska założycieli są zapisane na tablicy.
The founders' names are inscribed on the plaque.
In this case, "założycieli" is in accusative plural form, used to specify the individuals who are affected by the action of inviting.