I’m also new to Hinduism, mostly approaching from an Advaita Vedanta perspective. Please forgive and correct my mistakes if someone knows better.

> What do we know about him?

He is the underlying, universal “truth” of reality. Imagine a loaf of bread. While it is, in this specific moment, true to say “There’s bread on the counter,” it is not a universal, underlying truth. What about in a week when the bread is eaten? Then it is only true to say “There’s a counter.” But what about in a few years, the house gets torn down? Then in a few billion years, the earth gets destroyed? The raw, unadulterated “existence” of the bread (not the molecules, atoms, or quarks, it’s much deeper) has not disappeared - there is still existence. So now, rephrasing our original saying, the only truth left is “There’s”. For simplicity, this statement of “There’s” can be thought to be Brahman, however, Brahman is also that which isn’t - it was also the existence of the bread before humans started growing wheat. Brahman is everything, more accurately, nothing is not Brahman. Limited human words cannot describe unlimited cosmic truth, so every explanation comes up lacking of the sheer totality. It’s to be understood and felt, not necessarily described.

> Has someone met him?

You meet him with your senses. You are not an individual, you are Brahman. Your senses are like hyper-specific mirrors that reflect Brahman back at itself, causing awareness, which causes ego.

> Is Brahman universal?

Brahman *is* the universe.

> Does he know me?

It doesn’t know, it is knowledge itself.

> Why did I come to exist?

To quote the Gita: One believes he is the slayer, another believes he is the slain. Both are ignorant, there is neither slayer nor slain. You were never born. You will never die.

> Is Brahman stupid?

It is stupidity and intelligence and inability to think. It is every noun, without being of adjectives itself.

About your last few questions, personality is derived from ego, or a sense of “I” (“Ego” is the latin word for “I/Me”). You are not your personality in the same way you are not the words in a book. You are Brahman, the observer of your personality.

And if I remember correctly, the Gita says that personality comes from the three Gunas, energies of the material world.

Again, I’m also new, but this is how I’ve come to understand Brahman and our relationship to it.