check column has the same string

I would like to check if a dataframe column has the same string. for example, below dataframe in columns AAA, I want to check if all string is Jack, so the function call should return true!

import pandas as pd

data = {
    'AAA' :
    ['Jack','Jack','Jack','Jack','Jack'],
    'BBB' :
    ['January', 'February', 'February', 'April', 'January'],
    'CCC' :
    [85, 96, 55, 64,60]
}

df = pd.DataFrame(data)

print(len(df['AAA'].unique()) == 1)

unique can be used to check value is the same, but I need to check the string is Jack as well.