Given that the New Frontier stories are all written by Peter David, it should come as no surprise that every single character on this list is a Deadpan Snarker.
Mackenzie CalhounCaptain of the USS Excalibur. The first and, so far, only Xenexian in Starfleet. Born M'k'n'zy of Calhoun, he watched his father die at the hands of Danteri oppressors at a young age and eventually led his people to their liberation...all before the age of twenty. A chance encounter with one Captain Jean-Luc Picard set his path in motion to Starfleet, moving up through the ranks until the Grissom incident caused him to resign his commission (though he continued to work for Starfleet Intelligence on the DL). His nomination to command the Excalibur was met with much resistance, particularly with Admiral Jellico, but so far it seems to have worked out pretty well.
Elizabeth ShelbyElizabeth Paula Shelby first came to the attention of Starfleet higher-ups with her quick expertise on the Borg. After consulting with the Enterprise through the Locutus incident and the Battle of Wolf 359, she became first officer of the Chekov under Captain Morgan Korsmo, whom she would follow onto the Excalibur. When Korsmo was killed during the second Borg attack on Earth (in the events of Star Trek: First Contact), she was ready to move on to a captaincy when Admiral Jellico requested that she remain first officer so she could ride herd on Mackenzie Calhoun, with whom she had a relationship at the Academy. She eventually gets her own command in the Trident, then becomes an Admiral in charge of Bravo Station.
Burgoyne 172Burgoyne 172 is a Hermat, a hermaphroditic species, and chief engineer of the Excalibur. S/he is uninhibited in hir sexuality, and generally has affairs with several crew members at a time. When Selar became the CMO, s/he pursued her, but was rebuffed many times, until her pon farr reignited and she finally gave in to hir charms. This resulted in a son, named Xy after the captain's son (who was at the time missing and presumed dead). A short custodial battle ensued, after which the pair decided to raise him together. Promoted to first officer when Shelby gained command of the Trident.
SelarDr. Selar was a medical officer aboard the Enterprise for many years. During that time, she experienced pon farr, and returned home to mate with her chosen one...only to have him die of a heart attack while still in its throes. She covered her shock reasonably well, but her urges returned when she became CMO of the Excalibur two years later. After rebuffing Burgoyne's advances for a time, she finally gave into hir, and produced a son. A few years later, she became obsessed with finding a cure for her son's condition, to the point of kidnapping. She would eventually die trying to save the child she kidnapped from the Bretheren, while in the process uncovering a cure for her son's condition.
Robin LeflerOperations officer of the Excalibur and special liaison to Si Cwan after a tour on the Enterprise. Bright and cheerful; best known for her "Lefler's Laws" she started to impress her mother. Seems like the Only Sane Man...until her mother, whom she thought was dead, turns up alive in Thallonian space. Eventually falls in love with and marries Si Cwan, and serves as a Starfleet liaison to the New Thallonian Protectorate until she resigns her commission spoiler:after her husband was murdered by opposition forces. He did leave her Someone to Remember Him By, but that caused her even more trouble, sending her to Bravo Station for refuge.
Zak KebronChief security officer of the Excalibur. A member of the Brikar species. Known for his mighty strength and his Deadpan Snarker tendencies...at least until he molts; then he becomes quite a bit more verbose (and doubles as Excalibur's counselor).
Mark McHenryThe helmsman of the U.S.S Excalibur.
SoletaThe half-Romulan/half-Vulcan science officer of the ship. Soleta is the secondary protagonist of the series and one of the most important characters in the series. She would eventually leave Starfleet after her Romulan heritage was uncovered, and rise to prominence in the Romulan hierarchy, getting a ship right around the time of Star Trek: Nemesis.
Si CwanThe last remaining prince of the Thollonian royal family. He, alone, amongst them wasn't a complete scumbag. He attempts, throughout the series, to try and rebuild the Thollonian provinces into something resembling a functioning government. He succeeds.
Edward JellicoThe Starfleet Admiral of Deep Space Five and one of the direct supervisors of Captain Calhoun's mission.
JanosSecurity officer under Kebron. A genetically-bred mutant (who looks quite a bit like a mugato). He reverts to mindlessness in Stone and Anvil.
Kat MuellerOriginally the Executive Officer of the Grissom (she worked the night shift where Calhoun and the captain worked the day shift); was imported to the same position on the Excalibur. She would later become Shelby's first officer on the Trident, then promoted to captain when Shelby was promoted to admiral.
M'RessA character from the Star Trek: Animated series imported to the novels.
KalindaThe sister of Ci Cwan and one of the last remaining members of the Thollian royal family.
XyonA mysterious starship captain working in Thallonian space.
XyThe son of Selar and Burgoyne. Because of the conflict between his parents' genetics, he grows up extremely quickly; the three year time-skip between Stone and Anvil and After the Fall is long enough for him to grow up and become a Starfleet science officer. It's intimated he'll die just as quickly, thus causing Selar's parental conflict and would lead to her betrayal and death...and his possible salvation
Morgan PrimusAn immortal citizen of Earth who has a striking similarity to a number of Starfleet characters.