Alexander Rigby (1620-94) was the eldest surviving son of Alexander Rigby of Middleton in Goosnargh and brother of Edward. He married three times and succeeded his father to the Middleton estate on the death of the latter in 1650. In the Civil War he served at the siege of Lathom Hall during which he was taken prisoner. By the end of the war he had achieved the rank of colonel and was henceforth generally known as Col Rigby which helps to distinguish him from his brother Sgt Rigby (a sergeant at law not at arms). 
According to The History of Parliament:
Rigby enjoyed a strictly puritan education, and served under his father … during the Civil War. Unlike his father he was a Presbyterian, and held no office after the execution of the King, though he represented the county in Richard Cromwell’s Parliament … Rigby, who lived in one of the largest houses in Preston, was returned at the general election of 1660 by the corporation; but he lost his seat when the election was declared void without having taken any active part in the Convention [he was replaced by his brother Edward]. He does not seem to have conformed to the Anglican Church. He emerged from retirement to contest Wigan in February 1679, but without success … After the Revolution, Lord Brandon … made him a deputy lieutenant, probably in recognition of his brother’s political services. 
Henry Fishwick in his History of Goosnargh adds that ‘sometime previous to 1663 ‘he got into debt and had to mortgage property.’
A warrant issued in 1685 by the Earl of Derby for the arrest of Alexander and his brother Edward shortly after the beginning of the Monmouth Rebellion:
Having received intimation that Alexander Rigby of Middleton and Edward Rigby of Preston, Serjeant-at-Law, are persons disaffected to his Mtys government and of principles obnoxious to the public peace, and at this juncture not fit to be at large. These are to command you that you forthwith take into your custody the body of them and each of them, and keep a guard upon them in some convenient place till you receive further orders herein. Given under my hand and seal at Knowsley this 18th day of June, in the first year of his Mtys reign, 1685.
Fishwick adds that Edward Rigby was imprisoned in Chester castle but that ‘It is not known if his brother shared a similar fate.’