Colorado Springs Mayor John Suthers praised "two heroes" who helped pin down the gunman after he entered the club and opened fire.
"I think in the opinion of everyone involved, (they) saved a lot of lives," Suthers said.
The mayor said he had spoken to one of the men -- Richard Fierro, a 15-year veteran of the US Army, according to The New York Times.
"I have never encountered a person who had engaged in such heroic actions that was so humble about it," Suthers said. "He simply said to me, 'I was trying to protect my family.'"
In an interview with the Times, Fierro said he was at the club with his wife, daughter and friends watching a drag show when the gunfire began.
The 45-year-old Fierro, who was deployed to Iraq and Afghanistan during his military service, said he tackled the gunman by grabbing a handle on the back of his body armor, took his pistol and beat him with it.
"I don't know exactly what I did, I just went into combat mode," he said. "I just know I have to kill this guy before he kills us.
"I grabbed the gun out of his hand and just started hitting him in the head, over and over," he told the newspaper.
The attack was the deadliest on the LGBTQ community in the United States since a 2016 mass shooting at a nightclub in Orlando, Florida that claimed 49 lives.
GLAAD, an LGBTQ advocacy organization, noted that it came on the eve of the Transgender Day of Remembrance, which honors victims of transphobic attacks, and amid an uptick in hostility against the LGBTQ community in the United States.
"You can draw a straight line from the false and vile rhetoric about LGBTQ people spread by extremists and amplified across social media, to the nearly 300 anti-LGBTQ bills introduced this year, to the dozens of attacks on our community like this one," GLAAD president Sarah Kate Ellis said in a statement.
Colorado Representative Brianna Titone, an openly transgender state legislator, also singled out anti-LGBTQ rhetoric.
"When politicians and pundits keep perpetuating tropes, insults, and misinformation about the trans and LGBTQ+ community, this is a result," Titone tweeted.
Transgender rights were a hot-button issue in the United States leading up to midterm elections earlier this month, with Republicans putting forward a slew of legislative proposals to restrict them.
Colorado Springs police said five people were killed and 18 injured, 17 with gunshot wounds. Another victim was at the scene with "no visible injuries," according to an official statement.
Adrian Vasquez, the Colorado Springs police chief, said the suspect was armed with an "AR-style" rifle and a handgun.
The police chief condemned what he called an "evil act" and pledged to do everything he can to make the community feel safe again.
'They saved my life'
Bartender Michael Anderson praised the patrons who overpowered the gunman.
"There were some very brave people beating him and kicking him, stopping him from causing more damage," he said. "They saved my life."
President Joe Biden condemned the attack and spoke on Monday to Colorado Governor Jared Polis, who in 2018 became the first openly gay man elected as a US state governor.
"We must drive out the inequities that contribute to violence against LGBTQI+ people," Biden said. "We cannot and must not tolerate hate."
A man with the same name as Aldrich was arrested on June 18 last year after his mother said he had threatened her with a homemade bomb, according to a news release at the time from the El Paso County Sheriff's Office.
Vasquez, the police chief, said the suspect's mother was not cooperating with the authorities at this time.