I know a few.
All have gained a good inheritance. All have businesses. 1 inherited family business and then were left a lot by parents.
2 lived abroad in 1970s and then came home for 1980 boom time, made a packet. Both of these people did well in their companies, are in their 70s and bought good houses that are over 1 mill and invested when they could, inherited a bit, no kids.
1 is a property developer that took risks and invested. He's been very cautious and works hard (in his 60s won't retire, is a workaholic, worth over 10 mill but invested everything and lost it all few times).
My dsis isnt a millionaire but is well off. High earning couple, both with own houses (5 bed detached X 2) that they sold and bought big. Only 1 child and they invest carefully. Husband works away, owns company and brings in good bonuses. They have rental properties. They sacrifice a lot and push themselves very hard.
Good friend married a very high earner in the city.
I'm not well off but I inherited over 100k from a parent and will have another 3-400k coming our way from other parents estates. I'd rather have them here and not get anything! We have an income of £90k between us and don't live in an expensive area. We buy and have bought nothing on credit (except our mortgage). If we don't have the money in the bank we don't spend it. When our friends were putting things on credit and buying new cards on monthly payments we didn't. We worked and saved.
We invest 80% of anything we have that's extra, don't touch it and will use it to help out our DC.
We don't buy cars over 14k, we live in a standard, but nice, home and we're over paying on our mortgage to clear it in the next few years. We work very hard and we've never been on a holiday for more than 2k in 15 years. Our holidays are kept to under £1500 a year. We don't splash out often. We need a new kitchen, it will be nice but won't be expensive.
Oh and we bought our first house for £40k, sold it for £120k. We bought our current house for £170k, it's now worth over £300k. We've been extremely lucky and not found ourselves in a situation that financially we couldn't get out of with serious belt tightening and damn hard work.