REUTERS: In the ad entitled "Cruz Commander", a play on words on the Robertson family's duck call business Duck Commander, Robertson explained his criteria in endorsing a candidate.

Robertson said he looks for a candidate who is godly, who "loves us", is capable of doing the job and is able to kill a duck and "make a good duck gumbo", a traditional hearty soup in the southern U.S. state Louisiana, where Robertson lives.

"Cruz, the reason we're going to vote for you - all of us - is because you're one of us, my man. That's why we're voting for you. It's now or never," Robertson said to Cruz during the ad as the two men sat in a wooded area clad in camouflage face paint and clothes.

Robertson is the leader of the backwater Louisiana clan on the reality show about hunting, fishing and domestic squabbles.

In 2013, Robertson was suspended but later reinstated by A&E for his remarks to GQ characterizing homosexuality as sinful behavior.

"Duck Dynasty" merchandise, which ranges from sporting goods and apparel to camouflage furniture, has brought in some $400 million in sales, according to Forbes magazine.

Cruz leads Republicans in the runup to the Feb. Iowa Caucus, with businessman Donald Trump ahead in the New Hampshire contest scheduled for Feb. 9.