The old man died at age 58 after a long fight with cancer. Before that, he'd been an inventor, a manufacturer, the business manager of his family's photography studio, and an in-demand portrait painter. In the 50s, he'd been earning 10k per portrait in oils at a time when the average annual household income was just a few bucks above 3k. When he died, he left behind a handful of unfulfilled commissions.
Below is a quick sketch he did of himself. I would guess it was a few hour's work for him, given it's 'draft' look. It's a mere likeness that does not say a whole lot about his character.
I think the main reason dad could ask for and get a small fortune for each portrait he did was because he could capture and express someone's personality or character in them. When you look at one of his paintings, you immediately know what sort of person the subject was. Sometimes, you even get hint or two of their occupation. Sadly, the 'selfie' reproduced below doesn't say a whole lot about dad as a person. At least, not compared to his oil paintings.
According to mom, dad would have most likely called the sketch below, "Good draftsmanship, but not art".