The present paper begins by showing that if \(A\) is a commutative unital Banach algebra whose character space has cardinality greater than one, then there are families of arbitrarily large cardinality of pairwise non-isomorphic unital Banach algebras that contain \(A\) as a maximal abelian subalgebra. Motivated by this property, the authors address the following questions for an infinite-dimensional, commutative, unital Banach algebra \(A\): (i) How many pairwise non-isomorphic, closed, non-commutative, unital subalgebras \(C\) of \(\mathcal{B}(A)\) (the Banach algebra of all bounded linear operators on \(A\)) are such that \(A\) is a maximal abelian subalgebra of \(C\)? (ii) How many pairwise non-isomorphic, non-commutative, unital Banach algebras \(C\) are there that contain \(\mathcal{B}(A)\) as a closed, unital subalgebra and are such that \(A\) is a maximal abelian subalgebra of \(C\)? Concerning the first question, the authors show that in the case where \(A\) is an infinite-dimensional function algebra, \(A\) is a maximal abelian subalgebra of infinitely-many pairwise non-isomorphic closed subalgebras of \(\mathcal{B}(A)\). The authors give a significant answer to the second question by showing that there are compact spaces \(K\) and a family of arbitrarily large cardinality of pairwise non-isomorphic unital Banach algebras \(C\) such that each \(C\) contains \(\mathcal{B}(C(K))\) as a closed subalgebra and such that \(C(K)\) is a maximal abelian subalgebra in each \(C\).