Many have dedicated their lives to this question. Do we know for sure that bigfoot is real? Some say yes. Has it been 100% proven? Many say no.
Most people will not say bigfoot is real until there is a body to study and scientists say it is in fact a flesh and blood being. There are, however, many people out there that have seen this creature with their own eyes and believe, in fact, it is very real.
There have been written accounts of bigfoot/Sasquatch sightings for hundreds of years. Famous explorers to native americans have documented bigfoot sightings, in both oral and written history.
There are also thousands of accounts of sightings and footprint finds. Can these be hoaxes or misidentifications? Yes, absolutely. Do we feel that all of these fall in to those categories? No. The question you must ask yourself is, "How can all these prints and sightings all over the world be faked"?
We also have the famous film made by Roger Patterson and Bob Gimlin on October 20th in 1967. This too is a controversial piece of evidence. There are those that believe that this is an elaborate hoax and others believe this is absolutely the best piece of evidence in existence.