Leading the Proteas for the first time, Mulder's marathon innings propelled South Africa to a commanding 465 for 4 at stumps at Queens Sports Club. His effort is now the highest score ever by a player in their first match as Test captain, surpassing Graham Dowling's 239 for New Zealand in 1968.
Mulder, 26, is only the third captain in Test history to score a double century in his debut match in charge - and the first South African to do so. He also becomes the first Proteas player since Jackie McGlew in 1955 to score a century in his first Test as skipper.
The allrounder was handed the captaincy after Keshav Maharaj, who led the side in the first Test, was ruled out with a groin injury. Regular captain Temba Bavuma is recovering from a hamstring strain, while Aiden Markram was rested for the series, which falls outside the World Test Championship cycle.
South Africa were briefly under pressure in the morning session after debutant Lesego Senokwane (3) and Tony de Zorzi (10) fell early. But Mulder, coming in at number four, steadied the innings with David Bedingham, who played fluently for 82 off 101 balls. The pair added 184 for the third wicket.
After Bedingham fell to Tanaka Chivanga - Zimbabwe's most effective bowler on the day with figures of two for 85 - Mulder found an able partner in 19-year-old Lhuan-dre Pretorius. The teenager, fresh off a debut century last week, impressed once again with a composed 78 in a 217-run stand with his captain.
Pretorius fell shortly before stumps, caught by Wellington Masakadza off Kundai Matigimu, but not before helping to consolidate South Africa's firm grip on the match. Dewald Brevis (15 not out) joined Mulder at the crease and ensured no further wickets fell before the close.
Mulder's innings came off 259 balls and included 34 fours and three sixes, showcasing both patience and strokeplay. With South Africa already in a strong position and Mulder still unbeaten, the visitors will look to pile on further pressure on Day Two.
Wiaan Mulder broke the record for the Proteas' highest individual score in Test cricket after notching up an unbeaten 367 against Zimbabwe in Bulawayo before the visitors declared on 626-5.
A clinical Indian bowling display, headlined by a career-best performance from Akash Deep, dismantled England on Day Five of the second Test at Edgbaston, sealing a commanding 336-run victory to level the series 1-1.
Australia all-rounder Cameron Green was delighted to score 50 in the second innings of the second Test against West Indies and is hoping it's a sign his form is turning.
Lesego Senokwane and Prenelan Subrayen will both make their Test debuts as the Proteas made three changes for the second and final Test against Zimbabwe that starts in Bulawayo on Sunday.
