My guess is they asked you to interview on Google Hangouts or Yahoo messenger?
As Preston said protect yourself it's a scam. Also keep in mind that you are breaking TOS by accepting to have that check sent to you. It can get you suspended. Please report this client.
First: No, this isn't a legitimate offer.
Second: Don't ask about companies or clients by name. When scammers invite you to a job, they use fake names or names of real companies that they found on the Internet.
The names are meaningless. Nobody here has a list of "legitimate companies."
DO NOT GOOGLE the names of companies or clients. The scammers WANT you to google the names. Don't do it. That's part of how they trick you.
Judge offers by their Upwork history and by what they say in their job proposal, and by what they do during the interview. DO NOT think about the names.
I'm glad you decided to seek advice from the Community before making a mistake. No, you're not yet hired for the job and your client offered to pay outside the platform, which is a serious violation of our policy. This policy is there to keep our marketplace secure and to protect both freelancers and clients. We do ask our members to report job posts and clients offering direct payments.
To help you work safely on Upwork, please have at tips and warning signs shared in this thread.
Don't start working without an active contract, which would show in your "My Jobs" tab. You can find more details here.
You can find valuable information in the Getting Started as a Freelancer section of the Hep Center. I also advise reading the best practice advice shared by other users in following threads:
Thanks very much for your help. I will not communicate with these people anymore. Not a great first experience with Upwork having a scammer contact me. What do they hope to get from me? What is the link to the Upwork employer history?
They have no history because they get booted off the platform and just use a new email address to open a new account. They never hire. They target new freelancers because they know they haven't read or learned how the platform works. If you read the things Valeria shared with you, you will be able to realize these scammers immediately. Unfortunately since you are new you will probably get many more of these invitations. If you ever have any questions just come back here!!! Welcome.