Li Nalas was a leader of one of Bajor's many resistance cells during the Cardassian Occupation of Bajor. A revered war hero, he was considered by many to be the greatest Bajoran resistance fighter ever.
Early life and the resistance
Later, Li was part of a minor resistance cell. While the group was in hiding in the mountains, they were without food and power cells for their weapons and were forced down into the valley. Li was sent ahead to scout where he encountered Gul Zarale. When the other members of Li's group found the pair moments later; they believed that Li had killed the Cardassian officer in an intense duel, however the story wasn't quite true. In the actual event, he stumbled upon Zarale in his underwear, bathing in a river. The Cardassian was stunned and didn't react immediately and only when Zarale reached for his rifle, Li realized he still had his own phaser and fired at the Cardassian, killing him. Li didn't want to be a hero for doing such a thing but when he was discovered standing over the body and even after he tried to explain what had happened; no one believed him. Indeed, as Li and his follow resistance fighters travelled around, word of Li's exploits spread and grew to mythic proportions.
Li Nalas' career as a resistance fighter ended with his capture in 2360. Although his body was never found, he was presumed dead until 2370, when he was rescued from the Hutet labor camp on Cardassia IV by Major Kira Nerys of the Bajoran Militia and Miles O'Brien who posed as prostitute and her pimp, respectively, to gain access to the camp. (DS9: "The Homecoming")
After he and his fellow prisoners were rescued, Li was taken to Deep Space 9 where he was immediately recognized. He was very uncomfortable with his status as a hero and attempted to secretly leave the station for the Gamma Quadrant. Discovered by the crew of the departing ship, he was returned to Commander Benjamin Sisko. After Sisko questioned Li and pressed him for an explanation, he admitted that the stories of his heroism were largely based on myth. Li told the Commander the truth behind the myth that surrounded his reputation. As Li would relate to Sisko, he would never forget the embarassed look on the Cardassian officer's face as he died in his underwear. Li confided with Sisko that he had always felt uncomfortable with being an accidental hero. Sisko confronted Li with the unfortunate truth that Bajor needed a symbol; someone that the people could beleive in because the planet was on the verge of civil war. (DS9: "The Circle")
Shortly after his return to Bajor, Li was given both the title of Navarch and Kira's position as Bajoran liaison officer on board Deep Space 9, much to his embarrassment. Li assured the Commander that he would do his best to fufill his duties but that he could never replace Kira. This was done by Minister Jaro, who wanted to get Kira out of a position of power and to get Li off Bajor so that he would not influence Jaro's plot to take over the government. (DS9: "The Circle")
His rescue proved to be just in the nick of time, as he was able to play a pivotal role in preventing a disastrous coup d'état orchestrated by the Alliance for Global Unity. He helped rescue Kira from the insurgents, and helped defend the station against General Krim's troops, who attempted to take the station by force. After capturing Krim, Li was able to explain that the coup was being orchestrated by the Cardassians. Krim told his troops to stand down. Li was killed while saving Sisko from an attack by Colonel Day Kannu, and as a result, became a hero both in legend and reality. (DS9: "The Siege")
"Well, I consider myself something of a history buff and I must say some of the campaigns you led against the Cardassians were truly remarkable examples of tactical-"
"Doctor, I think you'll find that others enjoy talking about those days more than I do."
"Of course. I understand completely."
"I thought they'd have forgotten me by now."
"It appears you were wrong."
"This morning I was a slave and tonight I'm a hero."
"Where are you running to? This is Bajor. We're Bajorans. We fought a war to regain our homeland. How can you abandon it like frightened Cardassian voles? These ships are for our guests who must leave because it's no longer safe for them. We're Bajorans. I say we stay and solve our problems together. Are you willing to join me?"
"Off the hook... after all..."
The script for "The Homecoming" states the pronunciation of Li's name is "LEE NAH-less." Furthermore, it describes him as "a tall, rangy, laconic Bajoran in his late forties [...] a man of great physical presence, has a quiet self-effacing Abraham Lincoln/Gary Cooper charisma. He's intensely self-conscious; but years of living with his reputation has taught him to hide his true feelings behind his public image." 
The writers briefly considered having Li survive the final episode of the trilogy and become a recurring character. Both Peter Allan Fields and Michael Piller supported this idea; "It seemed to me that killing him would send us back to square one," said Fields, "Why go through three episodes with this guy, and then let him die? You're back as if he'd never been around. We could have written the whole thing without him." The final decision, however, came down to Ira Steven Behr, who believed that the character's death was truly necessary for the episode; "I just felt that this was a man who was living a lie, and at the end there needed to be a form of redemption, one that involved some self-sacrifice. The character was so impotent in certain ways, so out of his depth, and so clearly miserable as this figurehead. I think death really was, at that point, a blessing for him..." As executive producer, Behr also had the practical concers to think about. From a production standpoint, he didn't know how easy it would be to get Richard Beymer back to reprise the role, or how much it would cost to hire him. Ultimately, the writers decided they did need a someone to fulfill Li's role and so the character of Shakaar Edon was created in third season. (Star Trek: Deep Space Nine Companion, p. 83)
In their review of "The Siege", authors Mark Jones and Lance Parkin wrote of Li Nalas, "It's odd that they kill Li Nalas after so much build up. But this is another strong episode." (Beyond the Final Frontier, p. 193)