When the channel started its remit was to provide an alternative to the pre-existing channels (which at the time where BBC1, BBC2 and ITV). In doing so it sometimes overstepped the boundaries of acceptability (at least in some people's opinons) but it has arguably lead to a liberalisation of the UK tv industry.
One of the channel's strengths is its comedy. In the early days of the channel they showed "the comic strip" a series of hour long one-off comedies produced by a rotating lineup of alternative comedians such as Rik Mayall, Adrian Edmondson, Dawn French, Jennifer Saunders, Peter Cook, Peter Richardson and Alexi Sayle. Latterly they have showed cutting edge comedy shows such as Brass Eye and The Mark Thomas Product.
Channel 4 makes very few of the programmes it brodcasts. Its news service is supplied by ITN and it commissions many of it's programmes from independent producers.