Master
Every college has a leader, often called the Master (though half of the Masters are currently women, and some colleges have a Warden). The Master is the titular head of the college and its fellows and thus ultimately responsible for everything in the college. Masters often are provided gracious accommodations by the College and many (well-deserved) privileges.
Senior Tutor and Bursar
The second-in-command at a college from the perspective of academics is the Senior Tutor, who is responsible for the wellbeing of all the students in the college, both in terms of their academic and non-academic progress. From the perspective of administration, however, the second-in-command is the Bursar, who manages finances. The Bursar’s team also manages everything to do with accommodations and catering.
Other officers
The triumvirate of the Master, Senior Tutor, and Bursar are found in all colleges. Some colleges have other specialised posts, such as the Admissions Tutor, responsible for UG admissions, the Graduate Tutor, responsible for postgraduate students, the Music Tutor, responsible for musical training and productions, and so on.