He came from Scotland to Nova Scotia via England. At the tender age of 22 he settled in Halifax to continue his trade as a beer brewer with a reputation as a perfectionist.
Wanting to take his expertise even further Alexander Keith started his own brewery in 1820. As you can expect he would only use the best barley malts and the finest hops available, and all brewing was under his direct supervision.
Somebody that good at making beer very easily becomes a popular man, and Alexander Keith was no exception. He was twice elected Mayor of Halifax, served as a director for Bank of Nova Scotia and was the president of the legislative council. In fact, his birthday is still celebrated on October 5th every year.
The brewery is still in Halifax, brewing the beer in the same way, except that Alexander Keith is no longer supervising the brewing process.
His most famous beer is the famous "Alexander Keith's India Pale Ale", still one of the most popular beers in Nova Scotia, and highly regarded elswhere in Canada. It also has one of the catchiest slogans I've seen on any beer:
Those who like it, like it a lot.
Sources: Beer cans, bottles and http://www.keiths.ca/