This is the 14238th most frequent Russian word.
основателем
"Основателем" means "founder" in English.
Here, 'основателем' is the instrumental case of the noun 'основатель' (founder), indicating the person who did the founding.
Иван считается основателем этой компании.
Ivan is considered the founder of this company.
In this sentence, 'основателе' is the prepositional case, used because the phrase is responding to 'о' (about), referring to the topic or subject of conversation.
Она говорила об основателе движения, вдохновившего её.
She spoke about the founder of the movement that inspired her.
Here, 'основателям' is the dative plural form, used to indicate the indirect objects of the action of 'показать уважение' (show respect).