I've had two.
Kits Bo M. Was a Missouri Fox Trotter who stood for anything, wasn't phased by anything. My dad was riding him home from a trail ride and it was storming, a tree fell down literally right in front of them and Bo just kept on walking and stepped over the tree. Lol.
Arthur I have now, he's 23 and never spooks. I could run up behind him while he's sleeping and jump on him from his butt and he'd be unphased. I have videos of me galloping him bareback and bridleless, standing on him and jumping and sliding off bridleless, etc. In costume class we tested his bombproofness to the limit by making him a groom and me riding him as a bride with bells, ribbons, and a huge wedding dress. Never spooked