McHenry was born in Ireland and came to colonial Philadelphia in 1771; he studied medicine with Benjamin Rush, perhaps the best-known physician in early America.  He then entered a mercantile partnership with his father and brother in Baltimore, but when the Revolutionary War broke out, went into the Continental Army as a surgeon, later becoming one of Washngton's aides, and then an aide-de-camp of the marquis de Lafayette.  After he left the army in 1781, he served in the Maryland Senate and in the Articles of Confederation Congress.  He not only was at the Philadelphia Convention but also served in the Maryland ratification convention, and voted for the Constitution.  In the DHRC, the ediitors cite the following contemporary assessment of McHenry (Vol. XIV, 294), written by a correspondent to the Maryland Journal, 7th December, 1787: "Doctor McHenry acquitted himself to Admiration; -- he has shewn himself the Federalist, the Politician and the Gentleman, as well as the Citizen of this State. -- He compared and measured many Parts [of the Constitution at the Philadelphia Convention] objected to, with each other -- other parts of the same Instrument, and with other Propositions, as a graduated Scale, and ascertained their Differences as with Dividers.  I do no Man Injury, nor shall I give Offence, I believe, in saying his Knowledge of this Subject is the most comprehensive, his Ideas the most distinct, and his Explanations the shortest, clearest, and most satisfactory of any Gentleman's I have met with. -- I am really charmed with him."