Lived with man for 35 years. He passed in July 2019. I was beneficiary to 401k. He used my first name and his last. We were not married. What to do?

Sorry for your loss.  You may want to consider hiring a trusts and estates attorney to sort through this.  Designating someone as a beneficiary is supposed to avoid the headaches associated with probating a will, etc. but his use of your incorrect last name muddied the waters so to speak.  Hopefully you can provide sufficient documentation to prove that you are, in fact, the individual identified as the beneficiary.   Hope this helps. Jonathan R. Ratchik, Esq. Kramer, Dunleavy & Ratchik, PLLC 61 Broadway, Suite 2220 New York, NY  10006 (212) 226-6662 http://kdrpilawyers.com/