It can be of several different origins:
MacMullen (Scottish) in Ulster would be Mac Maolain
O'Mullan is Ó Maoláin
O'Mellan (Tyrone) is Ó Mealláin also called 'Mullan'.
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The spelling in the question is the correct spelling of the surname Sullivan.
Another answer:
If you are requesting the Irish form of the name: Ó Súilleabháin
For a male Ó Súilleabháin;
for a 'maiden name' Ní Shúilleabháin and
for a 'married name' Uí Shúilleabháin is the traditional female usage.