The Karankawa and Atakapan peoples, particularly the Akokisa, lived around Galveston Bay before European settlement. Spanish explorers charted and named the bay, and the pirate Jean Lafitte kept bases and hideouts around it until the U.S. Navy forced him out in 1821. Settlers came with Stephen F. Austin's colony and the Galveston Bay and Texas Land Company.
More about Pasadena
The final battle of the Texas Revolution was fought nearby on April 21, 1836. The main battlefield of San Jacinto lies in present La Porte, but Santa Anna was captured at Vince's Bayou in what is now Pasadena, and Pasadena and Deer Park call themselves the Birthplace of Texas.
Sam Allen started a 350-acre ranch in 1843. By 1888 the Allen Ranch covered 15,000 acres in Harris County, stretching from western Pasadena to Harrisburg, and 10,000 more in Brazoria County, with grazing land in Galveston and Fort Bend counties. Because cattle were often killed on the Galveston, Houston and Henderson Railroad, which crossed the ranch, Allen built a 19-mile fence along the tracks in 1875, from Harrisburg to League City, with a top rail wide enough to walk on. John H. Burnett of Galveston founded the town in 1893 and named it after Pasadena, California, for its lush vegetation.
Sources
Wikipedia: Pasadena, Texas