Mr. Bennet's first cousin, and second cousin to the five Bennet sisters. He marries Elizabeth Bennet's good friend and neighbor, Charlotte Lucas, and it is with them that Eliza stays when she goes to visit Kent.
Mr. Collins is the cousin of Mr. Bennet. He is twenty five years of age and holds a profession as a clergyman. The Longbourn estate is entailed on him, and so he will receive it when Mr. Bennet dies. He once proposed to Elizabeth Bennet, but she refused; and he later married Charlotte Lucas. He greatly respects his patroness Lady Catherine de Bourgh.
While he is the current heir to Longbourn, the estate of his distant, gentry cousin, Mr. Bennet; but if, before his death, one of Mr. Bennet's daughters should be able to present him with a grandson, said-grandson would then become the new heir of the entailment over a distant cousin, by virtue of being his closest living male blood relative (this is likely why Mr. Collins' late father, Mr. Collins Sr., before his death, urged his son to 'mend the rift' with the Bennets; if his son were to be the husband of one of Mr. Bennet's daughters, it would reinforce Collins' claim to Longbourn, and furthermore if he were to be the father of said-grandson).
We first meet Mr. Collins, when he comes to stay at the Bennet's house (which he is going to inherit, since he is the next living male). As soon as he walks into the house, we see him continually apologizing for minor incidents, even when he is told that it's all right, and frequently name-dropping his patroness, the even more hypocritical, and condescending Lady Catherine de Bourgh, even when it's getting obvious that he's being annoying. During the party at Mrs. Phillip's, he sucks up to every single rich person in the room, and constantly humiliates Eliza with his shallow and self-serving behaviour.
The next scene sees him proposing to Elizabeth, stating that "almost from the very moment I entered this house, I singled you out as the companion of my future life". He then gets rejected, but is not swayed as "it is common for a lady to reject the man she secretly means to accept", and asks her to reconsider, but her mind is made up. She will not have him. However, as soon as he hears negative reports of Eliza, he himself reconsiders, and decides not to marry Elizabeth. So, in order to boost his deflated ego, he sucks up to the Lucases, and eventually, Charlotte, the eldest of the Lucas children, and the dear friend of Eliza, agrees to marry him, against her better judgement.
Eliza's Stay In Kent
In March of the following year, Elizabeth visits Charlotte and Mr. Collins in their new home in Kent, which is called Hunsford. Their house is connected "only by a lane" to Rosings, the home of Lady Catherine de Bourgh. During the stay, Mr. Collins goes over to Lady de Bourgh's every day for dinner, and blindly follows any "advice" Lady de Bourgh gives. :)
The Rest Of The Book
After Eliza returns home, Mr. Collins is never seen in person in the novel again, but stays in the novel through letters sent to the Bennet household. When Lydia runs off, he advises Mr. Bennet to break off all relations with Lydia and her new husband Mr. Wickham, and to also 'forgive them".