My now legendary bone carver Mosus Praisetorch. Following a failed experiment with magma pressurization, a large portion of the magma tunnel access tunnel was covered in lava, to a depth in places of 1/7. The experiment was easy to clean up, just needed to wait until the lava evaporated or cooled. So I did; went back to other work, continued training weapon-/armour-smiths up to legendary, throwing parties, decorating trade goods, etc. Then I noticed, while looking through the units list, that Mosus was hunting for vermin. Annoyed and curious, I zoomed in and discovered that she was cut off from the rest of the fortress by the aforementioned 1/7 magma. Being a hardcore altruist still, I immediately set to work digging her out, whereupon she rushed to the food and booze stockpiles. I hovered over her, making sure she survived, and let her go to bed unbothered. I looked over her preferences, made her a statue in the metal she preferred, and installed an artifact cabinet in her fully-engraved room, by way of apology, and for a while afterwards I went easy on her, reduced workload and never worrying about her going on break.
Edit: Other than Mosus, I'm fond of one of my champion marksdwarfs, who has probably the most kills around, and the multi-legendary brewer/cook/grower who feeds and boozes the fortress.