Not named after my cat, or other favourite pet, or anyone else's favourite pet for that matter.
"Horatio the plastic lemming" was a small set of rubber bellows from a vandalised office typing chair. We used to amuse ourselves with the aforementioned item at my last place of work when the boss was (all too frequently) out of the office. The bellows kind of looked almost like a little creature, and when suitably compressed, could be forced to leap to their death from just about any high surface. This was all the more fun once we'd given 'him' a name. I don't know who came up with Horatio, but it stuck.
Anyway, along came the Internet, and message boards and the like. Every time I tried to sign up for something, I'd find that every name I ever wanted to use was already taken. I never felt comfortable adding numbers to a name that was already in use, as I always thought it'd be awkward if I bumped into the person whose name I'd 'stolen.' So, scraping the bottom of the barrel, I remembered poor old Horatio (he's in my loft somewhere) and used his name in tribute. Yes, okay, the 'tribute' thing is cobblers, but the rest is true.
When I signed up for RenaultForums, I didn't realise I was one of less than 100 users at the time and could probably have had any user name I liked. So Horatio it was. If you could change them and I could think of anything better, then I probably would have done by now