Robert Porrett Collier, 1st Baron Monkswell (June 21, 1817 - November 3, 1886), English judge, was born at Plymouth, and was the son of a prominent merchant of Quaker extraction.

He was educated at Oxford, was called to the bar in 1843, and went the western circuit. He obtained a high reputation by his successful defence of Brazilian pirates in 1845; they were, indeed, convicted at the assizes, but Collier ultimately procured their escape upon a point of law which the judge had refused to reserve.

He was elected member of parliament for Plymouth in the Liberal interest in 1852, and in 1859 was appointed counsel to the admiralty and judge-advocate to the fleet. In this capacity he gave in 1862 an opinion in favor of detaining the Confederate rams building in the Mersey, which would have saved his country much money and much credit if it had been acted upon. In 1863 he became solicitor-general, and in 1868 attorney-general, and in 1869 successfully passed a bankruptcy bill.

In 1871 he was appointed by Mr Gladstone one of four new judges upon the judicial committee of the privy council, although it was expressly provided by the act creating these offices that none of them should be filled by a law-officer of the Crown. This prohibition was evaded by making Collier a judge of common pleas, and transferring him after a few days to the privy council. This arrangement was unanimously condemned by public opinion, and gave the Gladstone cabinet a serious blow. He officiated, nevertheless, with distinction until his death, and was raised to the peerage as Baron Monkswell in 1885.

He was a man of many accomplishments, and especially distinguished as an amateur painter, frequently exhibiting landscapes at the Royal Academy and elsewhere. In his younger days he had been noted as a clever caricaturist.

He was succeeded in the peerage by his elder son, Robert (b. 1845), who, after taking a first class in law at Cambridge, went to the bar, and became (1871) conveyancing counsel to the treasury, and (1885-1886) an official examiner of the High Court, and, taking to politics as a Liberal, under-secretary for war (1895). The younger son, John Collier (b. 1850), inherited his father's artistic tastes, and became a well-known painter.