As a long-running Warhammer 40,000 universe work that blends action, comedy, and drama particularly well (while also having a constantly rotating supporting cast), Ciaphas Cain has many surprisingly popular minor and secondary characters.
- Among the semi-regulars, fans really like Sergeant Rock Lustig, his Unluckily Lucky subordinate "Jinxie" Penlan, and Reasonable Authority Figure General Zyvan.
- Sorel, the Cold Sniper from the first book is quite popular.
- Mira, Cain's Girl of the Week in the seventh book, has a modest fanbase for managing to be both a humorous Upper-Class Twit and a decent Action Girl at the same time.
- Alaric Tayber- the efficient Perlia PDF official who helps kick start Cain's rescue of thousands of people- and Badass Bureaucrat Scrivener Norbert from Death or Glory are both among Cain's more frequently-praised one-book allies. Mauve Shirt Demara from the same book also has her share of fans for being a Blood Knight who gets some touching bits of Character Development and a particularly sad death.
- Alaric's sister Felicia Tayber (who makes one reappearance after Death or Glory) appears to be very popular among fan artists, likely due to being the only canonically attractive tech priest in 40K and having a Genki Girl personality.
- Kayla and Donal are considered the most notable of Cain's commissar cadets in the sixth book.
- Sister Julien, the Perlia Battle Sisters inspector, made a surprisingly decent impression on fans in her one book.
- Amberly's....eccentric psyker Rakel is a minor member of her entourage but has her fans.
- Horatio Bugler and Igor Yaitz from the third book may be The Ghosts, but their dynamic Hero of Another Story naval exploits make for good reading and make them memorable to the fanbase.
- Well-Intentioned Extremist (with a heavy, heavy emphasis on the "extremist" part) Ernest Stavros Killian only appears in the final act of a single novel (with his existence barely even being hinted at before then), but his interesting past and Faux Affably Evil attitude before turning on Cain make him one of the best-remembered villains in the series.
- Tech-priest Logash and troopers Simla, Hail, and Lunt only appear in Caves of Ice, but have big fanbases for being decently fleshed-out characters who accompany Cain and his regular supporting cast for some of the series' most memorable and frightening battles.
- Surprisingly Elite Cannon Fodder Perlian militia fighters and Dad's Army expies Manrin, Jaq, and Franka only appear in two scenes of Cain's Last Stand, but are pretty well-liked.
- Chaplain Tope is only in a couple of scenes of The Last Ditch, but his Badass Preacher moments and status as a rare "emperor-bother" whom Cain can tolerate win him some fans.
- Modest Royalty (to varying degrees) governors Jona Worden (an Intrepid Reporter turned Young and in Charge Unexpected Successor) from the novella "Old Soldiers Never Die", Lio Trevellyan from Cain's Last Stand, Alaric [Du Panya=] from The Emperor's Finest, and Kerin from the short story "The Bigger They Are" are probably the most popular governors in a series with almost as many likable or competent governors as the rest of the Warhammer franchise combined.
- Anzibel only has a couple of scenes in Vainglorious, but is quite popular for being the first Necron in the Cain books to get a personality (and an interesting one at that, of haughty pettiness mixed with Pragmatic Villainy).
- Army Scout Calen from Dead in the Water and Dark Action Girl Malicia Mortalyss from The Devil You Know play large roles in the tie-in audio dramas' limited popularity.
- Friendly Enemy Gorok makes a decent impression throughout his surprisingly and regrettably few scenes in the first book.
- The two unnamed, We Hardly Knew Ye Ork Mooks from Caves of Ice who manage to engage in close-quarters combat with the Necrons (with one destroying a Necron and the other using a dismembered body part as a weapon) are probably more popular than any warboss in the Cain series.
