I've come to know Kali - or at least to understand her - later than other deities, but when I did it was a deep moment.
We are used to think about her like the Goddess of Destruction, but indeed she is more than that: she's a sort of primordial force, a fiery and fierce form of energy that can turn into a destroying calamity but it's essential for the world and life to react and renew themselves.
That one on the bottom is Lord Shiva, deeply connected with her.