16:9, 1.85:1, or 17:9 aspect ratio
It was nearly 30 years ago that I decided that HD should have 1080 image rows and square pixels, leading to today’s UHD 3840×2160 (16:9) and 4K D‑cinema 4096×2160 (~17.07:9). The 17 wasn’t my idea – I always thought that level of cinema should be based upon 1.85 · 2160 (16.65:9), ie exactly 3996×2160, but some standards committee members were worried that 3996 fell 0.1% shy of 4k.