Alfred has been the Wayne butler from the time that Bruce Wayne was but a boy. Alfred has always been faithful to the Waynes and has raised their son after Martha and Thomas Wayne's deaths. It was Alfred's leniency that allowed Bruce Wayne the ability to continue his mission. Alfred has always been Bruce Wayne's trusty Butler, the man who cleaned the Batcave, and mansion above single handedly. The trusted friend who not once revealed the identities of those of Bruce, Dick, Tim or even Jason. Alfred is the man waiting for the Batman with sandwiches when he returns from his battles with crime. The healer of wounds caused by the mission to turn Gotham, into a paradise.
That is of course not counting when he refused to let Bruce Wayne continue to destroy his body, (after the attack by Bane). When Alfred left he was visited by Nightwing, whom he has always thought should find his own way rather then follow in his mentor's steps. Nightwing and Alfred worked things out, and as Alfred realised, Batman needs Robin, Bruce Wayne needs Alfred.
Alfred started as a medic in the army, then as an actor, both of these qualifications Bruce Wayne needed for his guises as Batman. Alfred has been a mentor to Bruce Wayne, as it was he who taught Bruce the skills of, vocal mimicry, and the art of disguise, both arts that have aided the Bat greatly against his war against crime.
Alfreds first love was theater and he was a skilled thespian, these skills have been passed onto Bruce Wayne. Alfred is also familiar with the use of weapons though after his experiances he dislikes using them greatly. Every skill expected of a Butler is possessed by Alfred, and some that are not such as impersonationg ambulance men and telling Bruce Wayne who his guests are.
Alfred loves Bruce Wayne like a son, and there is a limit to how much abuse he can see Bruce subject himself to. His often acidic wit and sarcastic nature can be misinterpreted.