A serious caller is someone who calls Ghost to discuss the topics of the broadcast rather than to agitate the show. To the troll terrorists, they are known as "serious fags". A couple of individuals, notably Xarahox and Suspicious Tumbleweed tend to play passive-aggressive with Ghost, typically agreeing with him politically, but still agitate him 'for lulz' whenever they feel like doing so (Xarahox plays troll songs sometimes, Tumbleweed pulled off a call with Tri$ha that put Ghost in disarray).
Because Ghost's show was initially political, he had a small group of consistent listeners, who would call up and agree with him on topics he discussed during the show. Occasionally, when a troll, or Liberal was put on the phone, Ghost would bring in his 'backup' to get a debate moving forward, and to quickly defeat his opponent. Some serious callers had disagreements with one another, most notably Tzeki and Goofy_Bone, which developed into a 'contest' of sorts, to call in one after the other and degrade each other multiple times per show - much to the listener's delights.
A few serious callers are fan-favorites of the show (Tzeki and KaraszKun, especially as of the Return), as they call in, and either bash annoying callers and failtrolls, or have made themselves into fan favorites (Tzeki is a brony, and KaraszKun's Asperger's is a weak point for Ghost) all while actually discussing the topic at hand, not intending to derail it. Unsurprisingly, other serious callers are disliked by listeners, mainly due to the fact that they either don't interact well with trolls, or make it an agenda to attack Ghost's fanbase in 'defense' of him. They have caused much drama in the past on Twitter, and on the show. Examples during the 2011-12 episodes include Goofy Bone and Gasgara. After The Return, the controversial callers were G, Teutonic Plague and RaidenSnake, all of them were driven out of the show. Outed by trolls in the case of Raiden, messed up their relationship due to their own actions in the case of G or became trolls themselves in the case of Teutonic Plague.
A handful of Ghost's Serious Callers have their own BlogTalkRadio shows, and as a result, they get their own plate of attention from trolls, all in part due to the fact that their voice was heard on True Capitalist Radio. Debi Daly's set of trolls have taken a liking to Ghost, and assisted him in Troll War III (though Ghost has renounced his allegiance with them as of 2016, and has made active efforts to dox them).
For a list of such callers, refer to the page Category: Serious Caller.