Mateo is a former Coast Guard and former colleague of Caleb's where he was ranked higher and they had a professional rather than social relationship. He works as a miltary contractor. He is married to Renata and they have three children: Ariana (8), Alonzo (7), and Dante (2). The family is religious, and Mateo is quite strict with his older son. He is about 39 years old when he first appears in the story.

In July 2013, Caleb asks him to consider becoming Wynter's emergency caregiver should he win custody and then be deployed, and invites Mateo and his family over for a Fourth of July barbecue (02 Out of Tune). Wynter, who doesn't know the reason for the get-together, speaks out when she doesn't like the way Mateo appears to favor his daughter over his son, which upsets his wife.

After Caleb's medical discharge from the Coast Guard, Wynter asks Mateo in March 2014 to help him secure a job at his military contracting firm. Mateo surprises her by saying "We look out for our own," and gets Caleb the job (03 Rhythm and Rhyme). In October 2015 he comes to the Tiger Mountain house with a Schnoodle puppy that Caleb is hoping to adopt (09 Broken Strings).

Mateo went to Washington State, class of ’96, and supports the Cougars.

Mateo appears in 02 Out of Tune, 03 Rhythm and Rhyme, 09 Broken Strings.

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