Ильич is a patronym (son of Ilya). Lenin's father's first name was Ilya. It's not clear whether Иллич (pronounced differently) is related, apparently it's used

Ильич is a patronym (son of Ilya). Lenin's father's first name was Ilya. It's not clear whether Иллич (pronounced differently) is related, apparently it's used as a given name in some countries, or it might be an unrelated surname, or it might be a misspelling/mistranscription of the Russian patronym. Who knows!