So, I've started to play Dwarf Fortress only about a week ago, after delving deep into the wiki. I'm still playing the very first fort, which is now 11 years old. It just seems that i accidently chose a very easy spot to settle. The first underground cavern is 130 z-levels deep, and i've been able to easily kill and trap all those 100-goblin sieges that came along.
In the third year, i was attacked by a titan made out of black opal, throwing webs all over the completely featureless overworld (ok, there is a river, but there isn't even as much as a hill out there.) My fort only had like 50 dwarves at that moment, and i had no idea what to do. I drafted 20 dwarves into a makeshift militia and ordered it to attack the titan, which at that point had already killed 4 dwarves. As i had close to no weapons, those 20 dorfs started wrestling the opal titan, who, as i found out, had no problem stepping through the moat i created with the minimal knowledge i had. The battle reports came in, 2 more dwarves going down, but one of them somehow managed to bite the opal big toe off the titan. But all those bone bolts i have been crafting because i had no idea what else to do with the bones really came in handy when a series of lucky hits from my hunters were actually able to take down the titan. The last hit that caused the titan to go down was an masterfully crafted emu bone bolt by a brave hunter, who was from there on known as Ducim "Titan Slayer" Glazetwists, the Carnal Justice. He became the militia commander soon afterwards, nowadays being a legendary archer and marksdwarf.
Only a month later, we were attacked by a Werehorse. A short visit to the legends mode (yeah, with backups, call me cheap) revealed that probably about 2 percent of all living inhabitants of my world are werehorses at the moment. A longer visit to the legends mode revealed that the werehorse that attacked me was my former king and daddy of all the werehorses in the world. My militia was still active, so they tried to wrestle it to death. He took one of them down before changing back to his dwarven form, where he was quickly bitten to death by 17 rabid dwarves.
After i found out how the military and defense worked, only two dwarves living in my fort died in the last 5 years. I had to atom smash some caged dwarven werehorses, but those don't really count. One was my legendary cook, who died from a failed death pit experiment. No, he wasn't killed by the disarmed goblins and trolls. While trying to help, he accidently hit one of my Mace Lords with something (the reports aren't very clear on that) an the Mace Lord decided that clubbing his head into his upper body was the correct response to that.
At least i have to say that my new, 30 z-levels deep pit of doom with platinum floor is very good at killing caged goblins. I threw 150 of them down there in a single night. One of my dwarves even decided to create an artifact to remember this moment, which fittingly is a beautiful goblin bone weapon rack.
The second one died just a few minutes ago. He decided that it was a good idea to help the hunters in the caverns below and carry a corpse to the surface. The corpse he chose to carry was a crundle, which died just at the edge of the map. As soon as he picked it up, a Jabberer wandered onto the map right next to him, and within a nanosecond ripped his head clear off in his first attack. At this time, i wasn't even looking at the caverns, so i had no idea before the report came in that he was found dead deep below. I instantly switched down into the cave, but all i found next to him was a dead Jabberer, killed within a few seconds by noone other than the Ducim, the Titan Slayer, who decided to use his free time to hunt some subterranean creatures. Guess he just saw that giant thing and thought "Yup, seems reasonable to just kill it alone before the cavallery comes in." He then decided to slaughter a nearby troll and a herd of elk birds while someone else hauled the dead Jabberer up those 130 z-levels.