One of today's hottest real estate markets was home to a prominent sea captain, trader and politician who, more than a century and a half ago, amassed such fortune in the area's real estate he became one of the nation's first black millionaires.

In 1810, William Alexander Leidesdorff Jr. was born in the Dutch West Indies at St. Croix, Virgin Islands and, because of his complexion, the son of an interracial couple may not have been considered black until after he died and his origins were discovered. Some historic accounts indicate "passing for white" was his choice because he may not have otherwise been allowed to acquire such a fortune.

His father, William Sr., was a Dutch sugar farmer. Historic accounts vary about his mother's ethnic ancestry and say Anna Marie or Maria Spark was half either African or Afro-Caribbean and half European.

Leidesdorff began his career as a merchant sea captain first in New York and then in New Orleans where he became a wealthy cotton broker.

By 1838, the 28-year-old traded in his wealth for a 106-ton schooner, "Julia Ann," which he called home as he sailed the Pacific between the Sandwich Islands (Hawaiian Islands) and Yerba Buena (San Francisco), bringing sugar from the islands and returning with animal hides during a booming era of hide and fur trading.

In 1841, when an unruly California was "ruled" by Mexico and the first wagon trains of overland settlers were arriving at the far reaches of the continent, Leidesdorff put down stakes in Yerba Buena, where he launched the first steam boat the "Sitka" (for Sitka, Alaska, then Russian territory) in San Francisco Bay, according to Sue Bailey Thurman's biography of Leidesdorff, written for the Museum of the City Of San Francisco.

Naturalized by Mexico in 1844, Leidesdorff was granted 35 acres of land he dubbed "Rio De Los Americanos" on the left bank of the American River. The land grant was just across the river from what would be come a historic site -- indebted lumber merchant John Sutter's and eccentric wheelwright James Marshall's partially completed lumber mill, Sutter's Mill, the original site of gold discovery.

Leidesdorff would never cash in on the river area's skyrocketing land values, nor the sparkling yellow ore that pushed up values and prompted the 49er Gold Rush. Instead, Leidesdorff found his gold in Yerba Buena real estate. At one point he owned 360 lots, according to historic property records.

In 1846, he purchased a lot on what is now the corner of Clay and Kearny streets where he built a general store and later the city's first hotel, aptly dubbed "City Hotel". It was a watering hole for military officers until after the Mexican-American War. Later it became a sort of headquarters for gamblers and was also leased and sublet for stores and rooms, according to Zoeth Skinner Eldredge's The Beginnings of San Francisco.

Leidesdorff also built a warehouse, first to extend his trade business on what's now the corner of California and Leidesdorff, a street later named in his honor, Thurman says. The warehouse was later rented to the government as a quartermaster's warehouse.

The sea captain-turned real estate mogul, also built a lavish home, the most impressive in the area, on the corner of California and Montgomery Streets. Bank of America's striking International Headquarters Building now sits on that site.

During his stint as Vice Consul to Mexico, Leidesdorff often opened his home to visiting government officials, both American and Mexican, who enjoyed his hospitality and the only flower garden in Yerba Buena. Leidesdorff was also a member of the town's first council, served as town treasurer and was one of the three founding members of the first school board.

Also enjoying the sporting life, he staged California's first sanctioned horse race on a meadow near Mission Dolores where a plaque today marks his grave.

He died in 1848, at only 38, with an estimated worth of $1.5 million, but never lived long enough to enjoy his true wealth, more of which he would have held a year later when the discovery of gold made men wealthy in an instant and boosted land values in the valley of the American River.

Joseph Libbey Folsom, a historic U.S. Army captain, later traveled to the Virgin Islands, found Anna Maria Spark (when he discovered Leidesdorff's African ancestry) and paid her an estimated $100,000 to acquire Leidesdorff's holdings.

The transaction remained controversial until Folsom died in 1855. Sparks likely saw the sum as a tidy amount, but likely was unaware of the true value of her son's holdings.

Folsom enjoyed Leidesdorff's wealth only briefly, but left behind a greater memorial than Leidesdorff -- the town of Folsom, which at the time, stood on the site of Leidesdorff's former "Rio De Los Americanos" ranch.