This is the Inner Sphere, thousands of planets colonized by humankind. Once it was united under the Star League, but for the last three hundred years it has been consumed by savage wars...
— Adam Steiner, from the BattleTech animated series.
A galaxy-wide conflict with Giant Mecha spanning centuries is ripe for backstory, so FASA naturally encouraged filling out the BattleTech universe. They licensed the creation of a series of Science Fiction novels as the main medium for this. The continuity of these novels was incredibly well kept, mainly because the nature of the 'verse allowed for a very wide variety of characters and settings. Naturally, this led to an extremely large and diverse cast of characters, which is probably the strongest point of the novels. Much of the setting's tone was (and continues to be) defined by Michael Stackpole, with other authors fitting their works in around his.The novel series of the setting (which are far, far outnumbered by individual novels) include, in rough in-universe chronological order:
The Legend of the Jade Phoenix trilogy (Robert Thurston)
The Twilight of the Clans series (multiple authors, including Stackpole and Thurston)
The Capellan Solution duology (Loren L. Coleman)
The Fortress Republic duology (Coleman)
In addition, FASA licensed a number of video game series based on the universe. These, especially the MechWarrior series, turned out to be widely popular, and drew more people into the franchise.The video games include:
These works note tropes specific to the video games are listed on their pages provide examples of:
Absent Aliens: A few novels (most notably Far Country) actually do have aliens. The rest? None.
For Far Country, the aliens in question live in a system that's only been accessed by humans twice, both in jumpship mishaps that leave the humans stranded there. So they exist, but they can't interact with the rest of the Battletech universe.
Adaptation Decay: The animated series was retconed as an in-universe, "poorly reviewed Anti-Clan propaganda holo-vid".
A later sourcebook explains it as based on real in-universe events, but suffering among other things from Anachronic Order due to drawing inspiration from events that hadn't happened yet in the timeframe depicted.
Anyone Can Die: The EU encompasses a time span of over a century; if combat, accidents, or assassinations fails to kill someone, old age will.
Bullying a Dragon: Novel Close Quarters has the main character, Cassie, use a bolter on a battlemech to provoke it into chasing her. The metallic ping against the cockpit window is a direct insult to the mechwarrior's arrogance, which causes them to give chase. She runs through a few buildings before surprising the mech with an electrical attack to the knee joint. The electricity spot-welds the joint, and crashes the mech to on the ground. She repeats the same action later in the novel by attracting a mech into swampy terrain where it gets stuck and crashes onto the ground.
Bad Ass: Too many to list them all. It's pretty much a requirement for surviving the front lines in combat. Kai-Allard Liao is probably the most noteworthy example (see Memetic Badass below).
Canon Immigrant: As mentioned above, some of the Animated Series characters obtained this status. Adam Steiner is easily the most visible of them. Also of note are Vandervahn Chistu (Nicolai Malthus' superior) and Franklin Sakamoto. Chistu would briefly become one of the Falcon clan Kahns, ultimately dying at Vlad Ward's hands during the Refusal War. Sakamoto, on the other hand, would survive until the early stages of the Jihad in 3070. (Worth noting that Sakamoto was captured by the Black Dragon forces, with his ultimate fate apparently remaining unknown.)
Conspicuous CG: The cartoon's very poorly done BattleMech rendering sequences. Though they at least got the ponderous weight of 'Mechs right. The animated 'Mech combat looks like anime-style movement.
Critical Existence Failure: The concept of Combat Loss Grouping; stastistically, mechs of a similar weight class will continue to fight for long periods of time before becoming combat ineffective all at once.
Defector from Decadence: Trent of Clan Smoke Jaguar. Having been a victim of politics several times (his sibmate changes the official report of the battle of Tukayyid, and then manages to steal his spot on the Trial of Bloodright), with the help of his bondsman, he manages to escape his Clan, goes to Com Star and gives them the Exodus Road, the path to the Clan homeworld.
Dysfunction Junction: The Seventeenth Recon Regiment, aka "Camacho's Caballeros". Their top scout is a recovering sociopath, one of their best captains is a repeated rape victim, another is clinically insane (and proud of it), and their commander is grieving his deceased daughter while his surviving son suffers from "Well Done, Son!" Guy.
Everything's Louder With Bagpipes: The Northwind Highlanders have their bagpipe band play the loudest song possible onto Clan Smoke Jaguar radio frequencies to jam up the Clan's communications, forcing the Clanners to use more troublesome line of sight based communications.
Faking the Dead: Galen Cox. It's part of an elaborate scheme to expose Katherine Steiner-Davion's duplicity.
Good Colors, Evil Colors: Inverted in the animated series, under enhanced imaging Clanners look green while the Inner Sphere are red. Presumably because it's Clan tech that the "good guys" didn't have access to until halfway through the series.
Guile Hero: Adam Steiner, who in the animated series, considers accurate intel to be the most powerful weapon around and isn't above manipulating rival clans into fighting each other while his crew quietly escape.
Happily Married: Hanse might have married Melissa for political reasons, they did make it work and love each other.
Heel-Face Revolving Door: Tormano Liao. Basically, he's on whatever side is against the Capellan Confederation at the moment.
Kill It with Fire: One of the most effective anti-Mech weapons an infantryman can carry is the Inferno rocket, which is loaded with a napalm substitute that overheats the Mech and cooks the pilot inside. As a result, fear of death by fire is common among MechWarriors.
Memetic Badass: In-universe, Kai Allard-Liao. To the point where Clan commanders sending fifty Elementals to hunt him down (while he's injured, without a 'Mech, and on the run behind enemy lines), is considered a "fair fight".
Also subverted; the climatic action sequence of Grave Covenant and most of the 'Mech combat sequences that don't involve Morgan Kell or Yorinaga Kurita in the Warrior Triology appear to have been actually gamed out under the tabletop rules. The Grave Covenant scene with Victor's Daishi and Renny Sanderlin's Penetrator is even in one of the scenario books.
Sir Swearsalot: Clan pilots. Expect Clan character's dialogue to be about 20% cussing (in the Clan's vocabulary, which means loads and loads of "FREEBIRTH" and "STRAVAG" being yelled)
Stockholm Syndrome: POWs of the Clans start out as bondsmen, but are given the chance to regain their warrior status if they pass a Trial by Combat, upon which they become a fully fledged member of the capturing Clan. The most extreme example would be Phelan Kell a captured Inner Sphere mercenary (the Clans viewed these as the lowest form of scum) who not only earned his own bloodname (and by that, I mean he had a bloodname named after him), but would go on to become the leader an entire Clan subfaction.
Story Arc: Done by the animated series, which was noteworthy for American animation of the time.
The Reveal: The history of the Clans, and the nature of Wolf's Dragoons.
Their son, David Lear, was born shortly after they separated on Twycross, long before they got married. Kai was unaware he had a son for a while. So definitely earlier.
Also a very "star-crossed lovers" example in Victor Steiner-Davion and Omi Kurita. They fall in love with each other at just about first sight when meeting on Outreach, but he's the heir to the Federated Commonwealth and she's the daughter of the Coordinator of the Draconis Combine and they're both too conscientious to just shirk their responsibilities in the name of romance... They do get together in the end, although eventually an assassin sees to it that it doesn't last forever.