Mertil-Iscar Elmand was an Andalite warrior who was apparently trapped on Earth following the Andalite and Yeerk fight in orbit.
Unlike most Andalites, Mertil had an apparent allergy to the morphing technology, which resulted in him being unable to use it. This prevented him from healing himself when he lost half his tail in the crash-landing on Earth. Being unable to disguise himself as a human, he lived with his shorm and mate Gafinilan-Estrif-Valad, who had a fatal genetic disease.
Mertil was briefly captured by Visser Three as part of a plan to force Gafinilan to provide him with one of the 'Andalite Bandits'- Mertil and Gafinilan's health making them worthless as potential hosts, but they were able to double-cross Visser Three and save Mertil, who subsequently assured the Animorphs that he would take care of his mate. Marco later offered to visit Mertil and keep him company later on, an offer Mertil accepted.
- Though not mentioned directly, Michael Grant released later in a post about Diversity , that Gafinilan and Mertil were in fact a couple.