In the autumn of 1991, I took a job with a mathematical software company in Natick, Massachusetts. The office next to mine was dark most of the time, but I soon learned it belonged to an occasional visitor with a booming voice. Still based in California, he was not then working at the company full-time. But he had an important connection to it. His connection was this: without him the company would not exist. Cleve Moler created MATLAB, and MATLAB created MathWorks. Cleve Moler died last week. I cast my eyes downward, close them in respect and gratitude.

Cleve was many things, but above all he was a teacher. He loved teaching, and he was good at it. He could share exciting news about the singular value decomposition of symmetric matrices (spoiler: the singular values are simply the absolute values of the eigenvalues!), and before long you’d be excited too. But he was just as happy to coach you on optimal blackjack strategies or give you the inside scoop on the Great Pentium Bug of 1994. What he knew, he wanted you to know. What he knew was a lot.

What made Cleve such a good teacher? Why was he such an effective communicator? Was it the boom and gravel of that room-filling VOICE? Was it his carefully crafted MATLAB visualizations? Was it the depth of his insight or the pacing of his stories? We live in a world that wants to break things down into snack-sized tricks and techniques. “Five Hacks That Will Let You Teach Like Cleve Moler.” Friend, I will tell you. Here is Cleve’s hack: he cared. He cared about his material and he cared about you. He cared, and you felt it. If you can care like Cleve, maybe you can teach like Cleve. Most people can’t.

Cleve was curious and enthusiastic about the world, and he was willing to be your partner, your collaborator, your co-conspirator. He wasn’t remote, lecturing from a tower. He was there next to you, laughing and elbowing you in the ribs. He was with you, sharing the thrill of hard-won knowledge, dripping with raw insight.

The tools Cleve gave us, including MATLAB, were inspired by his teaching. Yet they proved to be not just instructive, but transformative, channeling a torrent of ideas from page to keyboard, bringing the world-changing power of linear algebra to more people than ever before. MATLAB opened a window on the world, streaming sunlight onto the clockwork of the universe. I am grateful for MATLAB. And so we might say that Cleve, too, was a window. Through such a person, we get a glimpse of the thrilling universe as they see it, and as we might wish to see it. The world he gestures to is more vivid than the one we see, fuller of possibility and delight. When he leaves the room, that vividness fades a little, falls from focus.

And so Cleve Moler has left the room. It is now for us to bring his curiosity, his fire, his care to our own lives and to those around us. When we meet the moment with that same delighted energy, we honor him. His vision was a gift. His presence was a gift. Thank you Cleve. Goodbye Cleve. We’ll miss you.