Jeremy Bentham (1748-1832) was a British political philosopher associated with the doctrine of utilitarianism, one of the foundations of political liberalism.
Bentham was descended from two generations of lawyers and his approach is legalistic, although he himself decided that the more useful question was how the law ought to be rather than what it actually was. He argues too that what his contemporaries were celebrating as 'natural rights' were little more than imaginary rights, and actual law created the only 'actual rights'. The French Declaration of the Rights of Man he described as 'nonsense on stilts' warning that to want something is not to supply it, that hunger is the same thing as bread.
Bentham saw the world as torn between two great forces, the quest for pleasure, and the avoidance of pain. From this, he intuited that it would be better to maximize the former and minimize the latter, and that all other considerations are irrelevant. This became known as the 'principle of utility', and Bentham's writings are a pure form of utilitarianism.
Bentham even saw himself in the role of spiritual leader of a kind of utilitarian movement, and donated his body (after his death) to University College London, (which he helped found) where it remains to today, preserved in a glass case.
His radical political advocacy included arguments for: the separation of church and state; freedom of expression; equal rights for women; the abolition of slavery; the abolition of physical punishment (especially that of children) and the abolition of the death penalty, and the decriminalization of homosexual acts.
His advocacy of economic freedoms and free trade is said to have influenced Adam Smith, and his social and political views had a strong effect, although not necessarily a simple one, on the development of liberalism by J.S. Mill and socialist ideas by Robert Owen.
What sort of person was Jeremy Bentham? In some ways a radical, an iconoclast and progressive, in others a reactionary, a die-hard and a killjoy. Probably the answer lies in his system - utilitarianism It is a doctrine that allows no space for individual taste, just as it allows no room for rights or duties, although Bentham allows that these may have socially desirable roles as convenient fictions. As he puts it in the opening sentence of Introduction to The Principles of Morals and Legislation: (1789):
The principle of utility judges any action to be right by the tendency it appears to have to augment or diminish the happiness of the party whose interests are in question... if that party be the community the happiness of the community, if a particular individual, the happiness of that individual.
It is actually in The Commonplace Book that the phrase 'the happiness of the greatest number can be found, Bentham writing that :""The greatest happiness of the greatest number" is the foundation of morality. The phrase actually originated slightly earlier with Frances Hutcheson (1694-1746) who had said: "That action is best, which procures the greatest happiness for the greatest numbers".
So Bentham's work ranges widely and it might seem erratically, at times. He spent much time and energy attempting to advance surveillance as the tool for a well-run society, even drawing up detailed plans for the construction of circular buildings where the actions of many could be watched and controlled by just one - 'the Inspector'. He considered his invention to be particularly suitable for prisoners, but the 'Panopticons', or 'Inspection Houses' are also, as the title page of Bentham's account makes it clear, applicable to any sort of establishment where people need to be kept 'under inspection', such as hospitals, factories, schools and 'mad-houses'.
The rewards from using 'the inspective force' as Bentham saw it, would be equally wide-ranging: "Morals reformed - health preserved - industry invigorated - instruction diffused - public burthens lightened - Economy seated, as it were, upon a rock - the Gordian knot of the Poor-Laws ... not cut, but untied"!
Bentham works it all out in enthusiastic detail.
To save the troublesome exertion of voice that might otherwise be necessary, and to prevent one prisoner from knowing that the inspector was occupied by another prisoner at a distance, a small tin tube might reach from each cell to the inspector's lodge, passing across the area, and so in at the side of the correspondent window of the lodge. By means of this implement, the slightest whisper of the one might be heard by the other, especially if he had proper notice to apply his ear to the tube." 
"it may be confined to the hours of study; or it may be made to fill the whole circle of time, including the hours of repose, and refreshment, and recreation.. To the first of these applications the most captious timidity, I think, could hardly fancy an objection: concerning the hours of study, there can, I think, be but one wish, that they should he employed in study. It is scarce necessary to observe that gratings, bars, and bolts, and every circumstance from which an Inspection House can derive a terrific character, have nothing to do here. All play, all chattering - in short, all distraction of every kind, is effectually banished ...
Jeremy Bentham also busied himself with a Plan for Universal and Perpetual Peace (1789) too. Undeterred by the lukewarm reception to his 'Panopticon', the plan is the same principle writ large, essentially relying on a supranational 'eye' to police the world - not by force of course, but by the free exchange of information, shaming any transgressor nations into line. Still, doubtless mindful of the political non-response to his Panpticon, Bentham became an active campaigner for the reform of the British political system, arguing the then radical case of 'one man, one vote'. And although most of the 'philosophical' arguments for experiments on animals are 'utilitarian', that is justified by saying that he benefits to humans outweigh the costs to animals, the 'father' of that school firmly against such arguments. In The Principles of Morals and Legislation, Bentham says firmly:
The day may come, when the rest of the animal creation may acquire those rights which never could have been withholden from them but by the hand of tyranny. The French have already discovered that the blackness of the skin is no reason why a human being should be abandoned without redress to the caprice of a tormentor. It may come one day to be recognised, that the number of the legs, the villosity of the skin, or the termination of the os sacrum, are reasons equally insufficient for abandoning a sensitive being to the same fate. What else is there that should trace the insuperable line? Is it the faculty of reason, or, perhaps the faculty of discourse? But a full-grown horse or dog is beyond comparison a more rational, as well as a more conversible animal than an infant of a day, or a week, or even a month old? But suppose the case were otherwise, what would it avail? The question is not, Can they reason?, nor Can they talk? but Can they suffer?'
- Bentham's Letter II