In its final season’s fifth episode, "Star Trek: Discovery" revealed L'ak as a member of the Breen, but costume designer Anthony Tran has been hinting at L’ak’s identity all along.
This mysterious warrior race first appeared in "Deep Space Nine." They were often clad in metal helmets with snout-like protrusions and green laser-like eye bands.
In a recent episode of "The Ready Room With Wil Wheaton," Tran talked about the costumes for Moll and L'ak, who were described to him as "a futuristic Bonnie and Clyde."
While biker gangs were the main inspiration for the duo's outfits, he also noted that he designed L'ak's getup with the Breen in mind after being told where the season was headed.
"The tubing that we also used in our Breen [...] this kind of coolant refrigeration thing," Tran explained, as he showed the details of the costume, clued to L’ak’s identity.
Writer Carlos Cisco also explained L’ak’s "refrigeration suits" on the podcast "The 7th Rule." He said that, over time, the Breen had evolved away from showing their "solid face."
In fact, the current version of the Breen has been nicknamed "the Jelly Breens," and like L'ak, these Breen can show off a funky gelatinous version of their own faces.
Since Tran knew L'ak was a Breen, his costumes nod to the "Deep Space Nine" version of them with the inclusion of diagonal metal tubing for a more updated take on the outfits.