Muir's new novel is Gideon the Ninth.
At Tor.com she tagged five sci-fi & fantasy books with bad old men, including:
Tó Neinilii from Storm of Locusts, by Rebecca RoanhorseRead about the other entries on the list.
This sequel to Roanhorse’s high-octane apocalypse ramble contains an old man whom I at first disliked, then liked again, and by the end realised was bad news beyond reckoning. If this was just a list of ‘old men who make you feel pain’ I’d put Tah, Kai Arviso’s wonderful granddad, but matchmaking Tah is an angel cake who only makes me feel pain in that I was terrified over his survival prospects. No, the bad old man of Storm of Locusts is Tó Neinilii, whose deceptively lighthanded appearance involves Hoskie and her travelling band of badasses encountering him while dealing with the White Locust. Tó wears pyjamas recreationally, lives on a houseboat, and forces Maggie Hoskie to make him a refreshing iced tea in the greatest power move of the series. To say that he is more than he appears is not a spoiler. To say that he is the surprising locus of some explosions I expect to see echo through the next book is, but I will say it anyway. Tó twinkles whimsically, chuckles more than once, and is responsible for Maggie’s group having to do an extended fishing minigame. In a very typical bad old man move he tries to give Maggie a metaphorical life lesson, but she’s genre-savvy and is having none of it. Great stuff.
--Marshal Zeringue