Even if you established a Revocable Living Trust while you are alive, it is likely that when you pass away you will have some assets that for one reason or another were never put into your Trust. Those assets may need to be distributed by your estate. To do so, you need a Will.
That type of Will is called a “pour-over Will” and it usually directs that everything you own should be transferred to your Trust. However, there are other things you might also need to accomplish with a Will, such as directing who should be appointed as a proper guardian for your minor children. You also might have some assets that you do not want to go through a Trust for other reasons.
An experienced estate planning attorney can advise you on creating an estate plan that fits your unique circumstances, which may or may not include a Will and a Revocable Living Trust.
Reference: Lake County News (Feb. 24, 2018) "The difference between a trust and a will."