The Walker Colt was the largest and most powerful black powder repeating handgun ever made. It was created in the mid-1840s in a collaboration between Captain Samuel Hamilton Walker (1817-47) and American firearms inventor Samuel Colt (1814-62), building upon the earlier Colt Paterson design. Walker wanted a handgun that was extremely powerful at close range.

Samuel Walker carried two of his namesake revolvers in the Mexican–American War. He was killed in battle the same year that his famous handgun was invented, 1847, shortly after he had received them. Only 1100 of these guns were originally made, which makes originals extremely difficult and expensive to obtain, going for US$150,000 or more at current estimates. On October 9, 2008, one specimen that had been handed down from a Mexican War veteran sold at auction for US$920,000.

The Republic of Texas had been the major purchaser of the early Paterson Holster Pistol (No. 5 model), a five shot cal .36 revolver, and Samuel Walker became familiar with it during his service as a Texas Ranger. In 1847, Walker was engaged in the Mexican-American War as a captain in the United States Mounted Rifles. He approached Colt, requesting a large revolver to replace the single-shot Aston Johnson holster pistols then in use. The desired .44-.45 caliber revolver would be carried in saddle mounted holsters and would be large enough to dispatch horses as well as enemy soldiers. The Walker Colt was used in the Mexican-American War and on the Texas frontier.

Medical officer John "R.I.P" Ford took a special interest in the Walkers when they arrived at Vera Cruz. He obtained two examples for himself and is the primary source for information about their performance during the war and afterward. His observation that the revolver would carry as far and strike with the same or greater force than the .54 caliber Mississippi Rifle seems to have been based on a single observation of a Mexican soldier hit at a distance of well over one hundred yards. The Walker, like most succeeding martial pistols and revolvers, was a practical weapon out to about fifty yards.

The Walker Colt holds a powder charge of 60 grains (3.9 g) in each chamber, more than twice what a typical black powder revolver holds. It weighs 4 1/2 pounds (2 kg) unloaded, has a 9-inch (229 mm) barrel, and fires a .44 caliber (0.454 in, 11.53 mm diameter) conical and round ball. The initial contract called for 1,000 of the revolvers and accouterments. Colt commissioned Eli Whitney Junior to fill the contract and produced an extra 100 revolvers for private sales and promotional gifts.

Problems with the Walker included its very large size, ruptured cylinders attributed to primitive metallurgy or (more likely) loading the original picket bullets backwards into the chambers and, an inadequate loading lever catch that often allowed the loading lever to drop during recoil, preventing fast follow-up shots. Period-correct fixes for this often included placing a rawhide loop around both the barrel and loading lever, to prevent the loading lever from dropping under recoil and locking the action.

Subsequent contracts beginning in 1848 followed, for what is today known among collectors as the 1st Dragoon, 2nd Dragoon, and 3rd Colt Dragoon Revolver models that were all based on the Walker Colt, enabling a rapid evolution of the basic revolver design. These improvements included 7 1/2 inch barrels, shorter chambers, typically loaded only to 50 grains instead of 60 grains, thereby reducing the occurrence of ruptured cylinders, and the addition of a positive catch at the end of the loading lever to prevent the dropping of the loading lever under recoil.

The Walker Colt was quite powerful, with modern replicas firing modern FFFg blackpowder producing energy levels in excess of 500 foot pounds with both picket bullets and 0.454 inch diameter (141 grain) round ball bullets. The black powder Walker Colt is regarded as the most powerful commercially-manufactured repeating handgun from 1847 until the introduction of the .357 Magnum in 1935, and has a muzzle energy nearly exactly the same as a 4-inch barreled handgun firing a .357 Magnum. The Walker Colt has long maintained a unique position and mystique among handgun users, and its name is often used as a common expression of any overly-large generic handgun example.

Modern replicas have been offered by the Colt Blackpowder shop and Uberti Firearms.