import re


def extract_character_name(actor_str):
    """Returns the character name extracted from the input string."""
    if not actor_str:
        return 'UNKNOWN'
    actor_str = actor_str.replace('(', '').replace(')', '')
    actor_str = actor_str.replace('[', '').replace(']', '')
    actor_str = actor_str.replace('van binnen', '')
    parts = re.split('[.,]', actor_str)
    return parts[0].strip()