Setheleyis th'Rasdeth (or Sethel for short) was an Andorian counselor in the mid-to-late 24th century. He died at the age of 58.

He had an unconventional approach to counseling, that helped Jadzia Dax in her decision to return to the Trill symbiont initiate program when she had been rejected by Curzon Dax. He and Dax would often visit Rio de Janeiro.

He was also a professor at Starfleet Academy. One of his students, Julian Bashir, took his class on "the benefits of positive visualization in psychotherapy".

He wanted nothing to do with the Dominion War and left the Academy and Starfleet in 2373 to set up a civilian practice near the Cardassian border.

In 2374, th'Rasdeth was on the transport Moon Zephyr when it was attacked by the Jem'Hadar. Sethel was killed and his body was brought to Deep Space 9 for identification. He had been due to travel to DS9 a month later, to meet Worf. (DS9 short story: "The Devil You Know")