Drew is the Dolans' horse, a willful and grumbly old thing. Okay, so he's just a horse, but he's got personality nonetheless. He always does what's asked of him, including long days driving Polly Ann and Tom into town for work only to go up to the Breen place at night and pull loads of lumber home. Poor guy. It's no wonder he cops an attitude from time to time. Here's one example:
The old horse was obviously disgruntled over having to leave home a second time in one day, so the made slow time. [….] They went up the sand hill beyond the bridge a step at a time, uttering sad groans. Tom humored him and when they got to the flat going beyond the hill Drew apparently became bored with his own behavior and broke into a trot without being asked. (36.15)
Drew also gives wonderfully astute observations on the quirks of humankind that could only come from an outside observer looking in on us as a group. For instance, after Tom neglects to provide Drew with any refreshment after their long night getting the chests from the Breen place, the text predicts that the old horse is probably "philosophizing on the unreasonableness of people" (52.16).
We don't hear much about Drew after Tom gets his new team, Molly and Dan, but we assume he goes into happy retirement in the new barn.