One firm has amassed more than 38,000 apartment units in markets including Phoenix, Tucson, Seattle, Anchorage, Colorado and Texas.
"They suck up all the big stuff that my other clients would like to buy, usually in a private sale before it hits the market," said Dan Benton, an Anchorage real estate agent.
Together, the Weidner Apartment Homes properties, founded by billionaire Dean Weidner, 72, have a net asset value of $2.3 billion.
Weidner owns more than 30 properties in Arizona, with at least 9,900 units, valued at about $1 billion before accounting for debt, according to data compiled by Bloomberg.
Half are in Phoenix, where rents are up 10 percent year-over-year, according to Trulia. Others are in Tucson, Anthem, Mesa, Chandler and Peoria, according to the website.
Most of the Arizona properties were purchased in 2010 or later.
"They're the 800-pound gorilla in town," said Kim Johnson, a real estate agent with Paragon Properties in Anchorage, where Weidner has 4,000 apartment units, or about 12 percent of the city's entire rental market.
Greg Cerbana, a spokesman for Weidner Apartment Homes, declined to comment. Andrew Kinstler, a partner at law firm Helsell Fetterman in Seattle, said in a phone call that Weidner didn't want to be featured in an article.
Weidner's mother began teaching him how to maintain and manage his family's duplex and fourplex apartments in Colorado Springs when he was 14 years old, according to a 2002 profile in Alaska Business Monthly. He continued to manage them through college, and bought his first property in Seattle in 1977, when he was an assistant vice president at Alaska Airlines.
His Kirkland, Washington-based company now owns at least 40 buildings with more than 6,100 units in Seattle and surrounding towns such as Bellevue, Kirkland, Renton and Everett. Rents in Seattle are up 6.4 percent over last year as of January, the real estate website Trulia shows.
"They recognize the opportunity in small markets," said Gary Klockenteger, senior vice-president of valuation advisory at Kidder Mathews in Seattle.
The company invests $400 million annually, adding 4,000 units a year, and Weidner reviews 20 to 30 purchase opportunities a week. It's the 30th-largest owner of rental properties in the United States, according to the National Multifamily Housing Council.
Some of the assets the company lists on its website are owned by limited liability corporations named after the properties or their addresses, according to public records. The records are filed under Weidner's name.
"While we continue to acquire and build new communities, we rarely sell our properties, providing consistency, and continuity for the long term," the company's website says.
The company has also invested in U.S. and Canadian housing markets, including Midland and Odessa, Texas, and cities in Alberta and Saskatchewan, where the shale oil boom created new jobs, and where falling oil prices now weigh on the local economies.
"They look for opportunity that most people would step right by," Klockenteger said.