Short answers, pulled from the story.
Bilbo Baggins is the title character and protagonist of J. R. R. Tolkien's 1937 novel The Hobbit. He also appears as a supporting character in The Lord of the Rings and is credited, within Tolkien's fictional framework, as the author of The Hobbit itself.
Gandalf chose Bilbo because he combined two bloodlines: the adventurous Took side and the steadier Baggins side. In a manuscript collected in the Unfinished Tales, Tolkien gave Gandalf the words: "I want a dash of the Took... and I want a good foundation of the stolider sort, a Baggins perhaps. That pointed at once to Bilbo."
The philologist Tom Shippey traced "Baggins" to the dialect words bæggin and bægginz spoken in Huddersfield, Yorkshire, meaning a substantial meal eaten between main meals, particularly at teatime. Tolkien had worked at the University of Leeds from 1920 and even wrote the foreword to a 1928 glossary of the Huddersfield dialect that recorded those words.
Ian Holm played the older Bilbo Baggins in The Fellowship of the Ring (2001) and The Return of the King (2003). Martin Freeman portrayed the younger Bilbo in Jackson's Hobbit film series, with Holm reprising the elder role in An Unexpected Journey (2012) and The Battle of the Five Armies (2014).
Medievalist Marjorie Burns argued that Tolkien based Bilbo on the Victorian designer William Morris, drawing on Morris's account of traveling in Iceland in the early 1870s. Morris was short, rotund, loved home comforts including a pipe and regular meals, looked out of place in wild country, and grew through his adventures, all traits he shares with Bilbo.
Bilbo is 111 years old at the start of The Lord of the Rings, celebrating what he called his "eleventy-first" birthday. He had kept the One Ring for sixty years since The Hobbit, and the ring had prolonged his life while leaving him feeling, in Tolkien's words, "thin and stretched".