There are many, many storied units in BattleTech lore & history, but one of the objectively coolest is the Royal Black Watch Regiment. Inspired by the real-world Scottish unit, the RBWR was formed alongside and/or patterned after the Northwind Highlanders. It became the bodyguard unit of the First Lord of the Star League, and would continue to recruit the best & brightest of the Highlanders throughout its existence.
When Stefan Amaris and his Rim Worlds Republic launched their coup and assassinated Richard Cameron in 2766, it was the Black Watch that was first to fight him, which ultimately led to the bulk of the unit being wiped out in a nuclear attack after they bitch smacked the taste out of the mouths of the Fourth Amaris Dragoons for far longer than they should have been able to.
Two weeks before the coup, the last commander of the unit, Colonel Hanni Schmitt, and several senior advisors met with Richard Cameron to share their concerns over the rising influence of Amaris, Unfortunately, Cameron chose to dismiss these concerns and ultimately had the leaders removed from his presence, fatally weakening the protection around him. It was Schmitt that lead personally led the Black Watch battalion against the Dragoons, sealing her fate in the blast.
That was not to be the end of the RBWR, however. Captain Elizabeth Hazen, along with four other members of the unit, escaped the destruction and formed a guerilla band called the Ghosts of the Black Watch. She led hit & run tactics, harassing the occupying Rim Worlds forces until General Aleksandr Kerensky and the Star League Defense Force could make it to Terra to avenge the fallen First Lord. Additionally, Schmitt's granddaughter Colleen, who had been raised on the ideals of the Black Watch, was herself an active member of the resistance to Amaris, linking up with the SLDF troops as they landed on Terra and providing first hand intelligence on targets of opportunity.
After the Liberation of Terra and the dissolution of the Star League by the remaining Great Houses, Kerensky would lead 85% of the SLDF and millions of civilians on his Exodus, which would ultimately culminate in his son Nicholas founding the Clans. Captain Hazen would eventually become the first Khan of Clan Jade Falcon, whilst Colleen Schmitt would be the first Khan of Clan Blood Spirit. In diametrically opposed movements, the Jade Falcons would become more antagonistic against Nicholas Kerensky when he chose to mingle his bloodline with Clan Wolf, whereas the Spirits, named for the espirit de corps that held together the first Clan warriors, would follow Kerensky's word as if it were the word of God Himself. It wasn't until the annihilation of Clan Wolverine that this situation would reverse when the Falcons would fall in line (after their own house cleaning known as The Culling) and the Blood Spirits would become more withdrawn after their censure for showing any sort of support for Clan Wolverine.
Meanwhile, back in the Inner Sphere, the Northwind Highlanders had become a mercenary force with the dissolution of the Star League. Maintaining their ties to the clan elders (descended from the Scottish Highland clans, not to be confused with Kerensky's clans), the unit took long term employment with the Capellan Confederation, and served admirably. They were one of the few units after Wolfs Dragoons arrival in the Inner Sphere to fight and defeat their famous Zeta Battalion.
That last until Hanse Davion launched the 4th Succession War and set out to cripple the CapCon. Offering Northwind independence, the Highlanders fought a brief conflict against themselves before accepting Davion's proposal.
Then the Clans invaded. I won't belabor to much there, except that Clan Jade Falcon was one of the Invader Clans, whilst Clan Blood Spirit (to a warrior elite as heck, but too small and with too little territory) was left back in the Clan Homeworlds. A descendant of Hanni Schmitt, Khan Karianna Schmitt does name a tank, the Morrigu, after the Schmitt Welsh legacy.
During House Liao's Operation Guerrero in 3057, Sun Tzu Liao would send Loren Jaffrey to the Northwind Highlanders. Jaffrey was a Capellan Death Commando whose grandfather had been a Highlander that chose to stay loyal to the CapCon during the 4th SW. Sun Tzu intended for Jaffrey to destroy the Highlanders from within but instead, he became a valued member of the unit, chosen to lead the Northwind Hussars after fighting against Clan Smoke Jaguar on Wayside in 3058 (pretty sure this is the same world that birthed The Fidelis several years later). The same year, the Second Star League was born and plans to destroy Clan Smoke Jaguar came together. The Highlanders were part of Task Force Serpent, the force sent to wipe out the Smoke Jags on their capitol of Huntress, in 3059.
Unknown to anyone until that point, the Highlanders had rebuilt the Black Watch Regiment in secret, and Captain Neil Campbell used the Huntress campaign to prove themselves to the new Star League. Using the vaunted RBWR insignia, the Highlanders enraged Clan Smoke Jaguar warriors who saw them as nothing more than pretenders to the title, ultimately causing a large portion of the force to be destroyed. But they prevailed, and upon returning to the Inner Sphere, the Black Watch once again become the First Lord's bodyguard unit.
This lasted until the Jihad, where the Black Watch was effectively destroyed as a combat unit at Dieron in 3069. Being the BAMFs that they are though, not even the Word of Blake could stop them, and Loren Jaffrey led the survivors of the unit to rescue Hohiro Kurita, heir to the Draconis Combine, from a Blakist prison on Dieron, once again reigniting the legend of the Ghosts of the Black Watch. The Word's Opacus Venatori, led by Precentor Berith, hunted the unit relentlessly, but it took until 3074 for them to finally catch up and kill Jaffrey, once again ending the Black Watch for a time.
Meanwhile, the Clan Homeworlds experienced the Wars of Reaving, a frenzied serious of conflicts that had started with resource grabbing in the wake of the Smoke Jaguars demise and that culminated in the death or exile of all but four Clans. Among the dead were the Blood Spirits, finally meeting their end in 3085 after two decades of fighting hard against Clan Star Adder. The Jade Falcons, on the other hand, would survive and thrive in their Inner Sphere holdings for several more decades...
The Jihad ended with the Blakest threat eliminated, and a new nation, the Republic of the Sphere, formed around Terra amongst the worlds once occupied by the Word of Blake, and that were once the heart of the Star League. The Northwind Highlanders were one of the first units to wholesale pledge their loyalty to this Republic, serving faithfully until the Republic's end...
Clan Jade Falcon and Clan Wolf battled the remains of the Republic's military on Terra, and once that was completed, fought each other for the right to be declared the ilClan, the Clan above all others. Wolf would ultimately win, gutting the Jade Falcon military. The survivors returned to Elizabeth Hazen's roots, forming the bodyguard unit of Alaric Steiner-Davion-Ward, the ilKhan, the First Lord of the Third Star League, and Khan of Clan Wolf. Countess Tara Campbell, nominal ruler of Northwind and leader of the Highlanders, was taken as a bondsman of Clan Wolf, but given over to the Jade Falcons to be their conscience, bringing the existence of the Royal Black Watch Regiment almost full circle.
With Tara a part of the Clan-led Star League, the role of Countess Northwind has fallen to her sister, Arabell Campbell-Stewart, with the 1st Kearney Highlanders fully reconstituted and led by Cadha Jaffrey. The Northwind Highlanders as a whole have returned to their mercenary status, recently (3151) hiring on with the Duke of Tybalt, Loren Hansen, the commander of Hansen's Roughriders, and have met Clan Jade Falcon in limited battle during a recon raid on the planet Caph.
So... It's just kinda interesting watching 40 years of BattleTech history play itself out through a dozen line developers and numerous different authors. I glossed over some points, obviously, but I find it really interesting that the Northwind Highlanders are one of my favorite mercenary units in the Lore, and that Clan Blood Spirit has been my favorite Clan since I started in the 90s, even if I play Wolf in the current era more. It's those little ties like this that made me fall in love with BattleTech in the first place.