Question: Who was the partner of the man who named Tower Rock?

Context paragraphs:
Tower Rock State Park: Tower Rock State Park is a state park near the community of Cascade in the U.S. state of Montana in the United States.  The centerpiece of the park is Tower Rock, a 424 ft -high rock formation which marks the entrance to the Missouri River Canyon in the Adel Mountains Volcanic Field.  It was well-known to Native Americans, and considered a sacred place by the Piegan Blackfeet.  Tower Rock received its current name when Meriwether Lewis of the Lewis and Clark Expedition visited the site in 1805.  Railroad and highway development in the late 1800s and 1900s skirted Tower Rock, but the landform itself remained pristine.  The 87.2 acre encompassing Tower Rock was added to the National Register of Historic Places on March 18, 2002.  The 140 acre Tower Rock State Park was created around the National Historic Site in 2004.

Tower Rock: Tower Rock, also known as Grand Tower, is a rock formation and landmark island in the Mississippi River, in Brazeau Township, Perry County, Missouri, near the town of Wittenberg, Missouri, and across the river from Grand Tower, Illinois.  It was listed on the National Register of Historic Places in 1970.

Tower Rock (disambiguation): Tower Rock is a landmark island in the Mississippi River, in Perry County, Missouri.

Federation Tower: The Federation Towers (Russian: Башня Федерации ) is a complex of two skyscrapers built on the 13th lot of the Moscow International Business Center (MIBC) in Moscow, Russia.  The two skyscrapers are named Tower East or Vostok (Russian: Восток; literally means "East") and Tower West or Zapad (Russian: Запад; literally means "West").  Vostok is a supertall skyscraper and is the tallest building in Russia, the tallest building in Europe, and the 36th-tallest building in the world, sharing that position with Central Plaza in Hong Kong.  Zapad is a shorter skyscraper than Vostok and is the 11th-tallest building in Russia.  The complex stands on the 13th lot, which has an area of 439,154 square meters.

Tower Buildings, Liverpool: Tower Buildings is a former office block in the city of Liverpool, Merseyside, England.  It stands with its longer front on the east side of the Strand, and extends round the corner into Water Street.  The building is located directly opposite the Royal Liver Building, which was designed by the same architect.  Earlier buildings on the site have been a sandstone mansion, and a later fortified house known as the Tower of Liverpool.  After this was demolished in 1819, it was replaced in 1846 by the first structure to be named Tower Buildings.  The present structure is one of the earliest steel-framed buildings in England, and details of its architecture reflect the earlier fortified building on the site.  It has been converted into apartments, and into units for commercial and retail use.

Spielberk Towers: Spielberk Towers are two high-rises in Brno, Czech Republic.  The towers are part of the complex Spielberk Office Centre.  The towers are named as Tower A and Tower B.  The lower tower is named Tower A and the taller tower is named Tower B.  The Tower A is 53 metres high and the taller Tower B is 85 metres high.  The taller tower has 21 floors above ground and 3 floors below ground.  The building has received a BREEAM Outstanding certificate.

Painted Rocks State Park: Tower Rock State Park is a Montana state park near the community of Darby.  Painted Rocks received its name from the green, yellow and orange lichens which cover the grey and black rock walls of the granite and rhyolite cliffs.

Meriwether Lewis: Meriwether Lewis (August 18, 1774 – October 11, 1809) was an American explorer, soldier, politician, and public administrator, best known for his role as the leader of the Lewis and Clark Expedition, also known as the Corps of Discovery, with William Clark.

Grand Tower, Illinois: Grand Tower is a city in Jackson County, Illinois, United States.  The population was 624 at the 2000 census.  The town gets its name from Tower Rock, a landmark island in the Mississippi River.

Wittenberg, Missouri: Wittenberg is an unincorporated community in Brazeau Township in eastern Perry County, Missouri.  It is located on the Mississippi River 14 mi southeast of Perryville.  Wittenberg is located in the Brazeau Bottoms on Brazeau Creek opposite Grand Tower, Illinois and Tower Rock, a landmark island in the Mississippi River.

Supporting paragraphs: Tower Rock State Park Meriwether Lewis
Answer: William Clark